Introduction to an Open Source Internet-Based Testing Program for Medical Student Examinations

The author developed a freely available open source internet-based testing program for medical examination. PHP and Java script were used as the programming language and postgreSQL as the database management system on an Apache web server and Linux operating system. The system approach was that a super user inputs the items, each school administrator inputs the examinees' information, and examinees access the system. The examinee's score is displayed immediately after examination with item analysis. The set-up of the system beginning with installation is described. This may help medical professors to easily adopt an internet-based testing system for medical education

Effects of Rapid Maxillary Expansion on Upper Airway; A 3 Dimensional Cephalometric Analysis

The purpose of this study was to use cone-beam computed tomography (CBCT) to assess changes in the volume and cross sectional areas of the upper airway in children with maxillary constriction treated by rapid maxillary expansion (RME). The study group consisted of 5 males and 9 females with mean age of 12.93 years with posterior cross bite and constricted maxilla who were treated with hyrax expander as part of their comprehensive orthodontic treatment. Pre and post RME CBCT scans were analyzed with 3D Dolphin 11.0 software to measure the retropalatal (RP) and retroglossal (RG) airway changes including volume and cross sectional areas. The transverse width changes were evaluated from the maxillary inter 1st molar and inter 1st pre molar mid lingual alveolar plate points. Pre and post RME scans were compared with paired t test and Pearson correlation test was done on data reaching significance. Only the cross sectional airway measured at posterior nasal spine (PNS) to Basion (Ba) level showed a statistically significant increase (P=0.0004). The minimal cross sectional area (MCA) was always found within the RP airway. The inter-molar and inter-premolar mid lingual alveolar plate distances increased equally by 4.76 mm and were statistically significant (P\u3c 0.0001). The percentage increase at the 1st premolar level was significantly larger than at the 1st molar level (P= 0.035). PNS-Ba cross sectional area increase was highly correlated with the maxillary 1st molar mid lingual inter alveolar plate width (p=0.0013). In conclusion, RME produced a numerically equal amount of expansion between the mid inter-lingual plates of maxillary 1st molars and 1st premolars. However, when the percentage change was calculated, a greater opening was observed at the 1st premolar level suggesting a triangular shape of opening. In regard to the upper airway, a moderate increase of the cross sectional area adjacent to the hard palate was found and this increase was deemed to be highly dependent on the expansion between the maxillary 1st molars. Further studies with a larger sample size and incorporating breathing evaluations are needed to estimate the real impact of the RME on the airway

Testing for Non-Nested Conditional Moment Restrictions Using Unconditional Empirical Likelihood

We propose non-nested hypotheses tests for conditional moment restriction models based on the method of generalized empirical likelihood (GEL). By utilizing the implied GEL probabilities from a sequence of unconditional moment restrictions that contains equivalent information of the conditional moment restrictions, we construct Kolmogorov-Smirnov and Cramer-von Mises type moment encompassing tests. Advantages of our tests over Otsu and Whang's (2007) tests are: (i) they are free from smoothing parameters, (ii) they can be applied to weakly dependent data, and (iii) they allow non-smooth moment functions. We derive the null distributions, validity of a bootstrap procedure, and local and global power properties of our tests. The simulation results show that our tests have reasonable size and power performance in finite samples.Empirical likelihood, Non-nested tests, Conditional moment restrictions

Stock Market Liquidity And Dividend Policy In Korean Corporations

The liquidity hypothesis predicts a negative relationship between stock liquidity and dividend payout propensity, i.e., a firm will decide to pay dividends to compensate for the liquidity demand of investors. This study comprehensively examines whether the liquidity hypothesis applies to the sample of Korean firms listed in the KOSPI and KOSDAQ markets. The main results of this paper are as follows. First, the dividend policy in Korean firms does not support the liquidity hypothesis, contradictory to the existing empirical studies. Next, the explanatory power of the liquidity hypothesis is even weaker for the KOSDAQ market, inconsistent with international evidence. Finally, even when we focus on the firm-year observations with non-negligible dividend payments, the liquidity hypothesis does not explain the dividend policy of Korean firms either. Our findings significantly contribute to the literature by robustly confirming the very limited role of the liquidity hypothesis for Korean financial markets. 

Simultaneous VLBI Astrometry of H2O and SiO Masers toward the Semiregular Variable R Crateris

We obtained, for the first time, astrometrically registered maps of the 22.2 GHz H2O and 42.8, 43.1, and 86.2 GHz SiO maser emission toward the semiregular b-type variable (SRb) R Crateris, at three epochs (2015 May 21, and 2016 January 7 and 26) using the Korean Very-long-baseline Interferometry Network. The SiO masers show a ring-like spatial structure, while the H2O maser shows a very asymmetric one-side outflow structure, which is located at the southern part of the ring-like SiO maser feature. We also found that the 86.2 GHz SiO maser spots are distributed in an inner region, compared to those of the 43.1 GHz SiO maser, which is different from all previously known distributions of the 86.2 GHz SiO masers in variable stars. The different distribution of the 86.2 GHz SiO maser seems to be related to the complex dynamics caused by the overtone pulsation mode of the SRb R Crateris. Furthermore, we estimated the position of the central star based on the ring fitting of the SiO masers, which is essential for interpreting the morphology and kinematics of a circumstellar envelope. The estimated stellar coordinate corresponds well to the position measured by Gaia

Photoluminescence from Si nanocrystals exposed to a hydrogen plasma

Si nanocrystals embedded in SiO₂films were exposed to an atomic H plasma at different temperatures. Photoluminescence intensity from the nanocrystals increases with increasing exposure time, followed by saturation that depends on the exposure temperature. The saturation level depends on the final exposure temperature and shows no dependence on the thermal history of exposure. This behavior is shown to be consistent with a model in which the steady-state passivation level is determined by a balance between defect passivation and depassivation by H, with the activation energy for the passivationreaction being larger than that for the depassivation reaction.This work was supported by Research Institute for Basic Science at Kangwon National University

One-dimensional broadband phononic crystal filter with unit cells made of two non-uniform impedance-mirrored elements

A one-dimensional finite-sized phononic crystal(PC) made of a specially-configured unit cell is proposed to realize broad bandpass, high-performance filtering. The unit cell is specially-configured with two elements having mirrored impedance distributions of each other. One element has a non-uniform impedance distribution that is so engineered as to maximize wave transmission in the pass band and to minimize transmission in the adjacent stop band while the other, exactly the mirrored distribution. The mirroring approach naturally yields the overall impedance contrast within the resulting unit cell, necessary to form stop bands in a PC of the unit cells. More importantly, the good transmission performance of the orginally-engineered element can be preserved by the approach because no additional impedance mismatch is introduced along the interface of the two impedance-mirrored elements. Extraordinary performance of the PC filter made of the proposed unit cell, such as high transmission, large bandwidth and sharp roll-off, is demonstrated by using one-dimensional longitudinal elastic wave problems. Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4790638ope

Time-varying effect of oil market shocks on the stock market

AbstractA mixture innovation time-varying parameter VAR model is used to examine the impact of structural oil price shocks on U.S. stock market return. Time variation is evident in both the coefficients and the variance–covariance matrix. The standard deviations of the demand side structural shocks reached forty year peaks during the global financial crisis and have remained high since. In the real stock return equation the coefficient of global real economic activity has declined since the late 1990s and that of oil-market specific demand oil shock has been lower since the early 1990s than before. The structural oil shocks account for 25.7% of the long-run variation in real stock returns overall, with substantial change in levels and sources of contribution over time. The contribution of shocks to global real economic activity to real stock return variation rose sharply to 22% in 2009 (and remains 17% over 2009–2012). The contribution of oil-market specific demand price shocks rose unevenly from 5% in the mid-1970s to about 15% in 2007, with a subsequent decline. The contribution of oil supply shocks has trended downward from 17% to 5% over 1973–2012