In the Republic of Korea, despite the introduction of one-dose universal varicella vaccination in 2005 and achieving a high coverage rate of 98.9% in 2012, the incidence rate has been increased sevenfold. This study aimed to investigate time trends of varicella incidence rate, assessing the age, period and birth cohort effects. We used national data on the annual number of reported cases from 2006 to 2017. A log-linear Poisson regression model was used to estimate age–period–cohort effects on varicella incidence rate. From 2006 to 2017, the incidence of varicella increased from 22.5 cases to more than 154.8 cases per 100 000. Peak incidence has shifted from 4 to 6 years old. The estimated period and cohort effects showed significant upward patterns, with a linear increasing trend by net drift. There has been an increase in the incidence among the Korean population regarding period and cohort despite the universal vaccination of varicella vaccine. Our data suggest the need for additional studies to address the current gap in herd immunity.

‘Healthy Twin’ is a twin family study extension of the existing Korean Twin-Family Register. Healthy Twin recruits adult like-sex twins over the age of 30 and their adult family members. Healthy Twin protocols are primarily tailored to the study of the quantitative trait loci of complex traits as well as to the role of environment in the etiology of complex diseases. A full-length survey is underway, including questionnaires, health examinations and the collection of biological specimens. So far, 820 individuals (169 twin pairs and their families) have participated in the survey and 1068 individual twins (608 twin pairs) have replied to the mailed zygosity questionnaire as of July 2006. The first phase (2005–2006) of Healthy Twin will recruit 1550 individuals (including about 380 twin pairs), and the second phase a proposed 1500 to 2500 additional participants. We report study protocols and zygosity and the distribution of family size of the study participants.

The Korean Twin Registry is the first nationwide twin study in Korea. We compiled 154,783 twin pairs from existing nationwide data sources, mainly from address and national health insurance data. The coverage of this registry was almost complete for the twins born since 1970, but less complete as age increased, so that there were only 990 pairs who were born before 1930. The twins' health examination (N = 54,390 persons) and questionnaire (N = 44,546 persons) results were incorporated into the registry, yielding 12,894 and 9074 concordantly informative pairs. Morbidity and mortality outcomes have been followed up since 1990, for most diseases. For preliminary analysis of complex diseases, we selected ventricular septal defects (VSD) in young twins, stomach and colorectal cancers in adult twins. We identified 353 VSDs, 284 stomach cancers, and 116 colorectal cancers among twins. The prevalence rates of cancers, but not that of VSD, were lower in twins than those in population. The difference in the cancer prevalence was marked for twins born before 1926, implying some degree of selection. Like-sex (LS) twins showed familial recurrence risks (λLS) of 41.2 for VSD and 22.4 for colorectal cancers, and 1.74 for stomach cancers. For opposite-sex (OS) twins, we could estimate λOS of 19.8 for VSD only. These results were compatible with previous studies for VSD and colorectal cancers, but not for stomach cancers. Despite the strength in size, availability of health outcomes, and some lifestyle and basic laboratory data, we need accurate zygosity information to improve the validity of the results.

This study investigated gender difference in the effects of social support, including emotional support and instrumental support (such as help when sick and financial assistance), and social activities on perceived health of middle-aged and older adults in South Korea. Data were acquired from 3771 men and 4954 women aged 40 years and older who participated in the 2005 cross-sectional survey of the Seoul Citizens Health and Social Indicators Survey. Using multiple regression analysis, both age- and gender-specific differences related to social support and engagement in social activities and self-rated poor health were examined. Poor emotional support from close friends, relatives or someone with whom one could talk about worries was strongly associated with poor self-rated health in men, with the greatest effect in older men. Lack of engagement in social activities was associated with self-rated poor health in older adults, especially in older men. Poor instrumental support was associated with perceived poor health only in middle-aged women. As a health improvement strategy for men aged 65 years and older especially, emotional support should be considered. Measures should be considered for encouraging social activities by older adults, particularly older men.

South Korea reported a total fertility rate (TFR) of 1·08 in 2005. This is the lowest level of all nations in the Organisation for Economic Co-operation and Development (OECD). Recently, the decline in the fertility rate has been a dominant phenomenon in Korea’s major cities. This study investigated the relationship between social environmental factors and fertility intentions for married women in Seoul, the capital of Korea, using a sample of 2211 married women who responded to the Seoul Citizens Health and Social Indicators Survey, 2005. Here, the effects of selected social environmental characteristics on fertility intentions are explored using multivariate logistic regression models. The relationships among a woman’s age, number of living children, job type, housing type, and social group participation were strong indicators of the intention to have additional children. Younger women living with fewer children generally have a higher intention to have additional children. Among women’s job types, blue-collar workers have a lower preference for additional children than white-collar workers and housewives. Married women participating in social groups have a lower preference for additional children than non-participants. Women’s participation in social activities appears to have various benefits, both individually and socially. However, whereas women’s participation in economic activities has been linked to questions of fertility in previous studies, the relationship between fertility and social activities has been downplayed. Women’s participation in social activities has increased over the past several decades, and the trend continues to grow. Therefore, women’s participation in social activities must be accepted as the status quo, and compatibility between women’s participation in social activities and childrearing needs to be increased. Consequently, a strong foundation for a fertility-friendly environment is needed, focusing on blue-collar workers and participation in social activities by married women.

Background: A fall experienced by an elderly person is of special note because it appears to hold a reciprocal causal association with the fear of falling. This study attempts to determine the temporal relationship between the fear of falling and falling among community-dwelling elderly.

Methods: Data on falls experienced during the previous three years were obtained from 732 community-dwelling elderly people. Participants were also asked to provide detailed information about their most recent fall, including the date, time of day, place, circumstances, consequences of the fall, fear of falling, and activity limitations due to fear of falling.

Results: Those who had fallen within the past six months had over four times greater odds of a fear of falling and approximately five times greater odds of activity restriction, compared with those who had not fallen. The association decreased linearly over time, and became nonsignificant for those who had not fallen during the past 25–36 months.

Conclusions: The experience of a fall is strongly associated with an increased fear of falling, and the association appears to persist for at least two years. An elderly person who has experienced a fall requires continuous attention to prevent the development of fear as another problem, together with early intervention to counter the fear of falling.

Diamond like carbon (DLC) coatings have attracted great attention for use in various applications in automobile industry and machinery because they have excellent properties such as low friction coefficient and ultra high strength. The low friction coefficient of DLC comes from anti-adhesion with other materials, smooth surface, lubrication of graphite structure at the contacting point of films, and the hydrogen content of the films. Many researches have been focused on the microstructure effects on the tribological properties of DLC films but few have been reported on the effect of hydrogen content. In this study, the effect of hydrogen content on the friction coefficient of DLC films has been investigated.

DLC films have been deposited on D2 steel by plasma enhanced CVD (Pulsed DC PECVD) method with different precursor gas of C2H2 and CH4 and different gas pressure. The effects of gas composition on the hydrogen content in DLC films and the resulting tribological properties have been reviewed. Si interlayer was deposited on D2 to improve adhesion of DLC on steel substrates. The characteristics of microstructure were evaluated by Raman spectroscope and composition was measured by RBS and EDS. The tribological behaviors of DLC films were investigated using ball on disk tribometer. The hardness of films was examined by nano-indenter. The failure mechanism of DLC deposited on steel substrates was examined using optical microscope and SEM/EDS. The results showed that the friction coefficient of DLC films deposited with C2H2 was 0.06 and that of the film with CH4 was 0.15. The friction coefficient improved with decreasing hydrogen content in DLC films.

For the better understanding of anti-wear properties of hard coating films, the effects of preferred orientation, surface roughness, and surface hardness on the tribological property of TiN and CrN films have been studied. TiN and CrN films were deposited by cathodic AIP (CAIP) with working temperatures of 350∼450°C, working pressures of 1∼5Pa, arc currents of 50∼90 A, and bias voltages of 30∼150V. The characteristics of microstructure and its effect on the friction coefficient were investigated with working conditions. The preferred orientation of the film was examined by XRD. The friction coefficient was determined using ball on disk tribometer. The preferred orientation of films was changed from (200) to (111) with decreasing working pressure and increasing bias voltage. It is reported that TiN coating with strong (111) orientation have better tribological property, but, in this study, although similar tendency was also found in TiN, the tribological property was increased with diminishing (111) orientation in CrN films. It is concluded in this study that the tribological property is not affected only by the orientation of the film, but it depends on the combined properties of surface roughness, surface hardness, and orientation of the film. The friction coefficients of TiN and CrN were 0.48∼0.52 and 0.49∼0.53, respectively.

A semi-empirical interatomic potential of the Ni–W system was developed using a modified embedded-atom method (MEAM) formalism including second-nearest-neighbor interactions. The cross potential was determined by fitting physical properties of tetragonal Ni4W available in the literature. The MEAM potential was used to predict phase stabilities, lattice constants, and bulk moduli of nonequilibrium and equilibrium phases in the Ni–W system. The results were in good agreement with experimental information or first-principles calculation.

We have grown well-aligned carbon nanotube arrays by thermal chemical vapor deposition at 800°C on Fe nanoparticles deposited by a pulsed laser on a porous Si substrate. Porous Si substrates were prepared by the electrochemical etching of p-Si(100) wafers with resistivities of 3 to 6 ωcm. These well-aligned carbon nanotube field emitter arrays are suitable for electron emission applications such as cold-cathode flat panel displays and vacuum microelectronic devices like microwave power amplifier tubes. Field emission characterization has been performed on the CNT-cathode diode device at room temperature and in a vacuum chamber below 10−6 Torr. The anode is maintained at a distance of 60[.proportional]m away from the carbon nanotube cathode arrays through an insulating spacer of polyvinyl film. The measured field emitting area is 4.0×10−5cm2. Our carbon nanotube field emitter arrays emit 1mA/cm2at the electric field, 2V/[.proportional]m. And they emit a large current density as high as 80mA/cm2 at 3V/[.proportional]m. The open tip structure of our carbon nanotubes and their good adhesion through Fe nanoparticles to the Si substrate are part of the reason why we can attain a large field emission current density within a low field. The field emitter arrays in our diode device are vertically well-aligned carbon nanotubes on the Si-wafer substrate.

High-quality Ta2O5 thin films for high-density memory devices were prepared at low temperatures by electron cyclotron resonance plasma-enhanced chemical vapor depostion (ECR-PECVD) without postannealing treatment. The effects of deposition temperature on the microstructure, composition, and electrical properties of the dielectric films were studied. The increase in deposition temperature from 145 °C to 205 °C improved the stoichiometry of the Ta2O5 thin films. As a consequence, EBD increased from 3.3 MV/cm to 4.4 MV/cm, and ∊Ta2O5, increased from 14 to 25. Interfacial SiO2 layer was observed by cross-sectional TEM, and its effects on the electrical properties of the overall dielectric film were also studied. The incubation period in which interfacial SiO2 grows was discussed with regard to reactivity between oxygen and Si substrate.