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Characterizing the Performance of a Resonance-Based MEMS Particle Sensor with Glass Beads
Ji-Seob Choi,Jinhong Noh,Hongsoo Choi,Yong-Jin Yoon,Woo-Tae Park 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.11 No.2
Fine dust measurement methods, such as weight change, beta ray measurement, light scattering, and resonance change, have been studied and used, but there is still room for improvement in terms of cost, system volume, and accuracy. In this study, we aimed to develop a low-cost, micro-scale, and highly accurate dust sensor using semiconductor processes. The sensor consists of a piezoelectric membrane with a diameter of 800 µm and a thickness of 2.8 µm. The resonance frequency and mode shape were measured and monitored using a Laser-Doppler-Vibrometer (LDV), and the resonance frequency shift was calculated based on the same mode shape. Vibration modes from (0,1) to (3,1) were observed within a 0–200 kHz frequency bandwidth. Spherical glass beads were used to measure resonance frequency shift for additional mass ranging from 0.863 to 4.52 µg. The first resonance mode (0,1) exhibited a clear proportional relationship between the resonance frequency shift and additional mass, while other modes exhibited non-proportional trends. Intriguingly, notable discrepancies in the resonance frequency shift emerged based on the spatial placement of the glass beads, even when the mass was the same. Additionally, we presented an approximate theoretical curve to portray the resonance frequency shift, which we subsequently validated against our measurement findings. This study presents a new attempt on the characterization method of piezoelectric mass sensors and provides a relatively simple and accurate analysis of the results.
Ryu, Jungho,Han, Guifang,Song, Tae Kwon,Welsh, Aaron,Trolier-McKinstry, Susan,Choi, Hongsoo,Lee, Jong-Pil,Kim, Jong-Woo,Yoon, Woon-Ha,Choi, Jong-Jin,Park, Dong-Soo,Ahn, Cheol-Woo,Priya, Shashank,Choi, American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.15
<P>Thick polycrystalline pure PbTiO<SUB>3</SUB> films with nano size grains were synthesized for the first time by aerosol deposition. Annealed 7 μm thick films exhibit well-saturated ferroelectric hysteresis loops with a remanent polarization and coercive field of 35 μC/cm<SUP>2</SUP> and 94 kV/cm, respectively. A large-signal effective <I>d</I><SUB>33,eff</SUB> value of >60 pm/V is achieved at room temperature. The measured ferroelectric transition temperature (<I>T</I><SUB>c</SUB>) of the films ∼550 °C is >50 °C higher than the reported values (∼490 °C) for PbTiO<SUB>3</SUB> ceramics. First-principles calculations combined with electron energy loss spectroscopy (EELS) and structural analysis indicate that the film is composed of nano size grains with slightly decreased tetragonality. There is no severe off-stoichiometry, but a high compressive in-plane residual stress was observed in the film along with a high transition temperature and piezoelectric response. The ferroelectric characteristics were sustained until 200 °C, providing significant advancement toward realizing high temperature piezoelectric materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-15/am5000307/production/images/medium/am-2014-000307_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5000307'>ACS Electronic Supporting Info</A></P>
CONTEXT MODELING FOR SERVICE COMPOSITION IN U-LEARNING ENVIRONMENT
Hongsoo Hur,Heeyong Park,Jeongseok Kim,Kyungwon Seo,Moohun Lee,Sunghoon Cho,Bonghoi Kim,Euiin Choi 한국멀티미디어학회 2007 한국멀티미디어학회 국제학술대회 Vol.2007 No.-
With advances in the field of ubiquitous technology, education configuration has changed to personalization and customization according to context of user. It is difficult to forecast previously and prepare relevant services, because context of individual is changed any time. Therefore, if we composite and provide users to relevant services with context information of individual, we will provide more customized services. To provide these service, we have to formulate context information of individual and represent it that computer can understand. Ontology-based approaches to context modeling have been proposed. Modeled context information can acquire high-level context information from low-level context data through reasoning rule. This paper proposes a context model to standardize basic context information for service composition in u-learning environment.
Choi, Hyoungshim,Jung, Young-Il,Kim, Hongsoo Elsevier 2018 International journal of nursing studies Vol.88 No.-
<P><B>Abstract</B></P> <P><B>Background</B></P> <P>Aggressive behavior is one of the most challenging behavioral psychological symptoms for older adults and their caregivers in nursing homes.</P> <P><B>Objectives</B></P> <P>The purpose of this study was to examine and identify contributing factors of aggressive behaviors among older adults in nursing homes in South Korea.</P> <P><B>Design</B></P> <P>This is a secondary analysis of a national survey on health and functional status among older nursing home residents.</P> <P><B>Settings</B></P> <P>Participants were recruited from 91 nursing homes.</P> <P><B>Participants</B></P> <P>A total of 1447 older adults were included for final analysis and they were randomly selected from a nationally representative sample of people 65 years and older at the sampled nursing homes.</P> <P><B>Methods</B></P> <P>Presence of aggressive behaviors was identified when participants showed at least one of the five symptoms in the Korean interRAI Long-Term Care Facility Assessment Tool such as physical abuse, verbal abuse, socially inappropriate or destructive behaviors, and resistance to care. Theory-based contributing factors were selected and examined. Multivariate logistic regression analyses were performed.</P> <P><B>Results</B></P> <P>About 19% of older nursing homes residents had aggressive behaviors, and several health and social factors including social engagement are associated with aggressive behaviors.</P> <P><B>Conclusions</B></P> <P>Aggressive behavior is prevalent in older nursing home residents with and without dementia in South Korea and individual and institutional level interventions are necessary.</P>