Inflated Standard Errors of MCMC Estimates in IRT

Two widely used algorithms for estimating item response theory (IRT) parameters are Markov chain Monte Carlo (MCMC) and the EM algorithm. In general, the MCMC algorithm has advantages over the EM algorithm - for example, the MCMC algorithm allows one to estimate the desired posterior distribution and also works more straightforwardly with complex IRT models. This ease of use, allows one to implement the MCMC algorithm without carefully consideration. Previous studies, Hendrix (2011) and Lee (2016), noted that the estimated standard errors from the MCMC algorithm are larger than those from the EM algorithm. Therefore, this study investigate the reason behind the larger standard error problem more in depth. In addition, it explores IRT parameter estimation in R including, including coding the MCMC method and using the mirt package for implementing the EM algorithm

Microstructual Characteristics Of Magnesium Metal Matrix Composites

Magnesium (Mg) Metal matrix composites (MMCs) reinforced by ceramic reinforcements are being developed for a variety of applications in automotive and aerospace because of their strength-to-weight ratio. Reinforcement being considered includes SiC, Al2O3, Carbon fiber and B4C in order to improve the mechanical properties of MMCs. Microstructural and interfacial characteristics of MMCs can play a critical role in controlling the MMCs’ mechanical properties. This study was carried out to understand the microstructural and interfacial development between Mg-9wt.Al-1wt.Zn (AZ91) alloy matrix and several reinforcements including SiC, Al2O3, Carbon fibers and B4C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy was employed to investigate the microstructure and interfaces. Al increase in hardness due to the presence of reinforcements was also documented via Vicker’s hardness measurements. Thermodynamic consideration based on Gibbs free energy was employed along with experimental results to describe the interfacial characteristics of MMCs. Reaction products from AZ91-SiC and AZ91-Al2O3 interfaces were identified as MgO, since the surface of SiC particles is typically covered with SiO2 and the MgO is the most thermodynamically stable phase in these systems. The AZ91-Carbon fiber interface consist of Al4C3 and this carbide phase is considered detrimental to the mechanical toughness of MMCs. The AZ91-B4C interface was observed to contain MgB2 and MgB2C2. In general, Vicker’s hardness increased by 3X due to the presence of these reinforcements

Long-term variation study of fine-mode particle size and regional characteristics using AERONET data

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).To identify the long-term trend of particle size variation, we analyzed aerosol optical depth (AOD, τ) separated as dust (τD) and coarse-(τPC) and fine-pollution particles (τPF) depending on emission sources and size. Ångström exponent values are also identified separately as total and fine-mode particles (αT and αPF). We checked these trends in various ways; (1) first-order linear regression analysis of the annual average values, (2) percent variation using the slope of linear regression method, and (3) a reliability analysis using the Mann–Kendall (MK) test. We selected 17 AERONET sun/sky radiometer sites classified into six regions, i.e., Europe, North Africa, the Middle East, India, Southeast Asia, and Northeast Asia. Although there were regional differences, τ decreased in Europe and Asian regions and increased in the Middle East, India, and North Africa. Values of τPC and τPF, show that aerosol loading caused by non-dust aerosols decreased in Europe and Asia and increased in India. In particular, τPF considerably decreased in Europe and Northeast Asia (95% confidential levels in MK-test), and τPC decreased in Northeast Asia (Z-values for Seoul and Osaka are −2.955 and −2.306, respectively, statistically significant if |z| ≥ 1.96). The decrease in τPC seems to be because of the reduction of primary and anthropogenic emissions from regulation by air quality policies. The meaningful result in this paper is that the particle size became smaller, as seen by values of αT that decreased by −3.30 to −30.47% in Europe, North Africa, and the Middle East because αT provides information on the particle size. Particle size on average became smaller over India and Asian regions considered in our study due to the decrease in coarse particles. In particular, an increase of αPF in most areas shows the probability that the average particle size of fine-mode aerosols became smaller in recent years. We presumed the cause of the increase in αT is because relatively large-sized fine-mode particles were eliminated due to air quality policies.Peer reviewe

Simulation study of dose enhancement in a cell due to nearby carbon and oxygen in particle radiotherapy

The aim of this study is to investigate the dose-deposition enhancement by alpha-particle irradiation in a cellular model using carbon and oxygen chemical compositions.A simulation study was performed to study dose enhancement due to carbon and oxygen for a human cell where Geant4 code used for the alpha-particle irradiation to the cellular phantom. The characteristic of dose enhancement in the nucleus and cytoplasm by the alpha-particle radiation was investigated based on concentrations of the carbon and oxygen compositions and was compared with those by gold and gadolinium.The results show that both the carbon and oxygen-induced dose enhancement was found to be more effective than those of gold and gadolinium. We found that the dose-enhancement effect was more dominant in the nucleus than in the cytoplasm if carbon or oxygen is uniformly distributed in a whole cell. In the condition that the added chemical composition was inserted only into the cytoplasm, the effect of the dose enhancement in nucleus becomes weak.We showed that high-stopping-power materials offer a more effective dose-enhancement efficacy and suggest that the carbon nanotubes and oxygenation are promising candidates for dose utilization as dose enhancement tools in particle therapy.Comment: 19 pages, 6 figures, 4 tables. presented to 7th KOREA-JAPAN Joint Meeting on Medical Physics (2014.09.25) accepted to Journal of the Korean Physical Society (2015.03.10

Stacked Antiaromatic Porphyrins

Aromaticity is a key concept in organic chemistry. Even though this concept has already been theoretically extrapolated to three dimensions, it usually still remains restricted to planar molecules in organic chemistry textbooks. Stacking of antiaromatic π-systems has been proposed to induce three-dimensional aromaticity as a result of strong frontier orbital interactions. However, experimental evidence to support this prediction still remains elusive so far. Here we report that close stacking of antiaromatic porphyrins diminishes their inherent antiaromaticity in the solid state as well as in solution. The antiaromatic stacking furthermore allows a delocalization of the π-electrons, which enhances the two-photon absorption cross-section values of the antiaromatic porphyrins. This feature enables the dynamic switching of the non-linear optical properties by controlling the arrangement of antiaromatic π-systems on the basis of intermolecular orbital interactions

Guidewire-catheter induced hydrodissection to assist radiofrequency ablation for subcapsular hepatocellular carcinoma with iodized oil retention in patients with failed artificial ascites due to perihepatic adhesion

PURPOSEWe aimed to evaluate the usefulness of guidewire-catheter induced hydrodissection (GIH) to assist radiofrequency ablation (RFA) for subcapsular hepatocellular carcinoma (HCC) with iodized oil retention in patients with failed artificial ascites due to perihepatic adhesion.METHODSThis retrospective study included 17 patients with small subcapsular HCC ineligible for ultrasonography-guided RFA who received RFA under guidance of fluoroscopy and cone-beam computed tomography immediately after iodized oil transarterial chemoembolization (TACE) between April 2011 and January 2016. In the study patients, creation of artificial ascites to protect the perihepatic structures failed due to perihepatic adhesion and GIH was attempted to separate the perihepatic structures from the ablation zone. The technical success rate of GIH, technique efficacy of RFA with GIH, local tumor progression (LTP), peritoneal seeding, and complications were evaluated.RESULTSThe technical success rate of GIH was 88.24% (15 of 17 patients). Technique efficacy was achieved in all 15 patients receiving RFA with GIH. During an average follow-up period of 48.1 months, LTP developed in three patients. Cumulative LTP rates at 1, 2, 3, and 5 years were 13.3%, 20.6%, 20.6%, and 20.6%, respectively. No patient had peritoneal seeding. Two of the 15 patients receiving RFA with GIH had a CIRSE grade 3 liver abscess, but none had complications associated with thermal injury to the diaphragm or abdominal wall near the ablation zone.CONCLUSIONGIH can be a useful method to assist RFA for subcapsular HCC with iodized oil retention in patients with failed artificial ascites due to perihepatic adhesion

Liver Laceration with Hemoperitoneum after Cardiopulmonary Resuscitation

It is well known that external chest compression during cardiopulmonary resuscitation is frequently associated with various complications. These complications predominantly involve trauma to the heart, lungs, and chest wall, whereas cases involving intra-abdominal injury are much less frequent. The present report describes a rare case of a female patient with severe hemoperitoneum associated with liver injury after cardiopulmonary resuscitation. Although emergent angiography and embolization of the hepatic artery were performed and transfusion of various kinds of blood products was done continuously, the patient expired the next day