Prediction of mechanical properties of Al alloys with change of cooling rate

The solidification process significantly affects the mechanical properties and there are lots of factors that affect the solidification process. Much progress has been made in the research on the effect of solidification on mechanical properties. Among them, the PF (Phase Field) model and CA (Cellular Automata) model are widely used as simulation methods which can predict nucleation and its growth, and the size and morphology of the grains during solidification. Although they can give accurate calculation results, it needs too much computational memory and calculation time. So it is difficult to apply the simulation to the real production process. In this study, a more practical simulation approach which can predict the mechanical properties of real aluminum alloys is proposed, by identifying through experiment the relationship between cooling rate and SDAS (Secondary Dendrite Arm Spacing) and mechanical properties. The experimentally measured values and the values predicted by simulation have relatively small differences and the mechanical properties of a variety of Al alloys are expected to be predicted before casting through use of the simulation

VLBA 24 and 43 GHz observations of massive binary black hole candidate PKS 1155+251

PKS 1155+251 is a radio-loud quasar source at z=0.203. Observations using very long baseline interferometry (VLBI) at ~2, 5, 8 and 15 GHz show that the structure of the radio source is quite complicated on parsec scales and that the outer hot spots are apparently undergoing a significant contraction. Because these results cannot be fully explained based on the compact symmetric object (CSO) scenario with a radio core located between the northern and southern complexes, we made observations with the Very Long Baseline Array (VLBA) at 24 and 43 GHz to search for compact substructures and alternative interpretations. The results show that the radio core revealed in the previous VLBI observations remains compact with a flat spectrum in our sub-milli-arcsecond--resolution images; the northern lobe emission becomes faint at 24 GHz and is mostly resolving out at 43 GHz; the southern complex is more bright but has been resolved into the brightest southern-end (S1) and jet or tail alike components westwards. Explaining the southern components aligned westward with a standard CSO scenario alone remains a challenge. As for the flatter spectral index of the southern-end component S1 between 24 and 43 GHz in our observations and the significant 15 GHz VLBA flux variability of S1, an alternative scenario is that the southern complex may be powered by a secondary black hole residing at S1. But more sensitive and high-resolution VLBI monitoring is required to discriminate the CSO and the binary black hole scenarios.Comment: 7 pages, 3 figures, accepted by MNRA

A Dynamic Information-Based Parking Guidance for Megacities considering Both Public and Private Parking

The constantly increasing number of cars in the megacities is causing severe parking problems. To resolve this problem, many cities adopt parking guidance system as a part of intelligent transportation system (ITS). However, the current parking guidance system stays in its infant stage since the obtainable information is limited. To enhance parking management in the megacity and to provide better parking guidance to drivers, this study introduces an intelligent parking guidance system and proposes a new methodology to operate it. The introduced system considers both public parking and private parking so that it is designed to maximize the use of spatial resources of the city. The proposed methodology is based on the dynamic information related parking in the city and suggests the best parking space to each driver. To do this, two kinds of utility functions which assess parking spaces are developed. Using the proposed methodology, different types of parking management policies are tested through the simulation. According to the experimental test, it is shown that the centrally managed parking guidance can give better results than individually preferred parking guidance. The simulation test proves that both a driver???s benefits and parking management of a city from various points of view can be improved by using the proposed methodology

New-type of Multi-purpose Standard Radon Chamber in South Korea

Radon is an inert and a radioactive gas which is colorless, tasteless and odorless. As the radon decay proceeds, and if DNA damage continues beyond repair capacity of cells in the human body, it can cause severe health problems such as lung cancer in the long-term. There is a tendency that those countries where legal restriction on radon is strict, various studies related to radon are under way. In South Korea, radon has been regulated under recommendation level. Even though there are about 3 standard radon chambers in Korea, they have not been in an active use because of lack of demand. Also, most of them are specialized in calibration of radon detectors only. Recently, Korean government started giving some attention to radon issue and supporting radon research fields. Thus, this study was carried out to develop a new type of radon chamber for multi-purpose such as 1) radon emission rate from natural and artificial radon sources; 2) calibration of radon detectors; 3) evaluation of radon mitigation efficiency. Keywords: Radon, Radon Chamber, Indoor Air Quality, Chamber Desig

Estimates of Discharge Coefficient in Levee Breach Under Two Different Approach Flow Types

The amount of released water (discharge) in a levee breach is a primary input variable to establish an emergency action plan for the area next to the levee. However, although several studies have been conducted, there is still no widely applicable discharge coefficient formula; this needs to be known to estimate discharge amount through an opening caused by a levee breach. Sometimes, the discharge coefficient developed for a sharp crested side weir is used to rate the discharge, but, in case of a levee breach, the resulting geometry and flow types are similar to that over a broad crested weir. Thus, in this study, two different openings—rectangular and trapezoidal shape—are constructed in the center of a levee at a height of 0.6m to replicate levee breach scenarios, and the effect of two different approach flow types—the river type approach and reservoir type approach—are explored to suggest a discharge coefficient formula applicable for discharge rating for a levee breach. The results show that the ratio of head above the bottom of an opening and the opening width is a key variable for calculating the discharge coefficient of a reservoir type, but the approach Froude number should also be considered for a river type approach. The measured data are used to improve rating equations and will be useful in the future to validate computational fluid dynamics simulations of wave propagation during levee failure into the inundation area

Time-resolved photoluminescence of the size-controlled ZnO nanorods

Size dependence of the time-resolved photoluminescence (TRPL) has been investigated for the ZnO nanorods fabricated by catalyst-free metalorganic chemical vapor deposition. The nanorods have a diameter of 35 nm and lengths in the range of 150 nm to 1.1 mum. The TRPL decay rate decreases monotonically as the length of the nanorods increases in the range of 150 to 600 nm. Decrease of the radiative decay rate of the exciton-polariton has been invoked to account for the results

Direct activation of Transient Receptor Potential Vanilloid 1(TRPV1) by Diacylglycerol (DAG)

The capsaicin receptor, known as transient receptor potential channel vanilloid subtype 1 (TRPV1), is activated by a wide range of noxious stimulants and putative ligands such as capsaicin, heat, pH, anandamide, and phosphorylation by protein kinase C (PKC). However, the identity of endogenous activators for TRPV1 under physiological condition is still debated. Here, we report that diacylglycerol (DAG) directly activates TRPV1 channel in a membrane-delimited manner in rat dorsal root ganglion (DRG) neurons. 1-oleoyl-2-acetyl-sn-glycerol (OAG), a membrane-permeable DAG analog, elicited intracellular Ca2+ transients, cationic currents and cobalt uptake that were blocked by TRPV1-selective antagonists, but not by inhibitors of PKC and DAG lipase in rat DRG neurons or HEK 293 cells heterologously expressing TRPV1. OAG induced responses were about one fifth of capsaicin induced signals, suggesting that OAG displays partial agonism. We also found that endogenously produced DAG can activate rat TRPV1 channels. Mutagenesis of rat TRPV1 revealed that DAG-binding site is at Y511, the same site for capsaicin binding, and PtdIns(4,5)P2binding site may not be critical for the activation of rat TRPV1 by DAG in heterologous system. We propose that DAG serves as an endogenous ligand for rat TRPV1, acting as an integrator of Gq/11-coupled receptors and receptor tyrosine kinases that are linked to phospholipase C

Thermal plasma flow and equivalent circuit analyses on the electrical coupling of a DC-RF hybrid plasma torch

Numerical analyses on the electrical coupling of a DC-RF (direct current – radio frequency) hybrid plasma torch are conducted on the basis of magneto-hydrodynamic flow and equivalent circuit models to find the dependency of coupling efficiency on RF frequency and confinement tube radius. Computations are also carried out for the inductively coupled RF plasma torch to make a comparison between their calculated results. Numerical results reveal that the electrical coupling efficiencies of the RF and DC-RF hybrid plasma torches have a similar dependency on RF frequency with an almost constant difference of slightly higher efficiencies for the hybrid plasma, due to the relatively linear frequency dependency of equivalent circuit parameters as well as the resultant radially expanded DC-RF hybrid plasma toward the confinement tube wall compared with the RF plasma. But it is found that the reduction in the confinement tube radius less than some critical value, for instance 22 mm in this numerical work, possibly causes the coupling efficiency of the hybrid plasma to drastically deteriorate compared with that of the RF plasma. Such poor efficiency of the hybrid torch with relatively small radius is attributed to a significant diminution of the high temperature region upstream between the DC torch exit and the first induction coil segment, which means that the reduced tube radius may lead to an ineffective superposition of DC arc jet and RF plasma. As a result of the reduced high temperature region, the magnetic flux linkage is decreased for the smaller confinement tube, which leads to a drastic decrease in the electrical coupling. As the confinement tube radius becomes smaller, the re-circulation eddies under the DC torch are almost destroyed by a DC arc jet and a stagnation region formed is contracted to the central region. This contracted stagnation region prohibits the convection heat transfer by re-circulation of sheath gas flow from the coil zone to the upper part of the confinement tube, which ultimately results in a significant diminution of the high temperature region in the upstream. The present numerical analyses indicate that a special focus need to be brought into the influences of the DC arc jet on the electrical and thermal flow characteristics of the DC-RF hybrid plasma in determining the torch dimensions for effective conversion of RF power into plasma