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Unraveling the Intercalation Chemistry of Hexagonal Tungsten Bronze and Its Optical Responses
Lee, Yonghyuk,Lee, Taehun,Jang, Woosun,Soon, Aloysius American Chemical Society 2016 Chemistry of materials Vol.28 No.13
<P>In an attempt to promote energy saving through the clever control of varying amounts of visible light and solar energy in modern buildings, there has been a surge of interest in the novel design of multifunctional glass windows otherwise known as smart windows. The use of chromogenic materials (e.g., tungsten oxides and their alloys) is widespread in this cooling energy technology, and for the case of hexagonal tungsten oxide (h-WO3)-based systems, the overall efficiency is often hindered by the lack of a systematic and fundamental understanding of the interplay of intrinsic charge transfer between the alkali-metal ions and the host h-WO3. In this work, we present a first-principles hybrid density-functional theory investigation of bulk hexagonal tungsten bronzes (i.e., alkali-metal-intercalated h-WO3) and examine the influence of the intercalation chemistry on their thermodynamic stability as well as optoelectronic properties. We find that the introduction of the alkali-metal ion induces a persistent n-type electronic conductivity, and dramatically reduces the optical transmittance (down to similar to 28%) for infrared wavelengths while maintaining fair optical transparency for next-generation electrochromic devices in very energy efficient chromogenic device technology.</P>
In search of non-conventional surface oxidic motifs of Cu on Au(111)
Lee, Taehun,Lee, Yonghyuk,Kang, Kisung,Soon, Aloysius The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.10
<P>Growing ultrathin oxide layers on metal surfaces presents a new class of low-dimensional nanomaterials with exceptional chemical and physical properties. These 'new oxides'' can be used in many niche technologies and applications such as nanoscale electronics and heterogeneous nanocatalysis. In this work, we study the formation of surface oxidic structures and motifs of Cu, supported on the Au(111) substrate, using first-principles density-functional theory calculations in conjunction with an ab initio atomistic thermodynamics model. In particular, we systematically examine and analyze the detailed atomic structure and surface energetics of various oxidic motifs of Cu on Au(111), in particular, p2, p2s, p2(6q6) and the newly suggested metastable p2(6q6) + O-3, in comparison to both the binary O/Cu(111) and O/Au(111) systems. Depending on the oxygen atmosphere and the type of surface defects introduced in the oxidic layer, various non-conventional, non-hexagonal surface oxidic motifs of Cu could be obtained. Our theoretical results agree with recent scanning tunneling microscopy (STM) experiments and we propose that metastable non-hexagonal surface motifs may pave a way to pursue further studies of these interesting complex surface oxidic layers on various metal supports.</P>
Polytypism in Hexagonal Tungsten Trioxide: Insights from Ab Initio Molecular Dynamics Simulations
Lee, Yonghyuk,Lee, Taehun,Soon, Aloysius American Chemical Society 2018 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.122 No.37
<P>Temperature-dependent microstructural evolution of hexagonal WO<SUB>3</SUB> (<I>h</I>-WO<SUB>3</SUB>) polytypes is explored via ab initio molecular dynamics calculations within the density-functional theory framework. We present simulated finite temperature radial distribution function and X-ray diffraction patterns to reinterpret recent experimental pair distribution function analysis. This work clearly demonstrates that after a more careful analysis of the finite temperature structural properties of <I>h</I>-WO<SUB>3</SUB>, an intermediate H1-like structure is predicted at higher temperatures, while the more stable H4 polytype (and not the experimentally suggested H2 polytype) is obtained nearer ambient temperatures. This is further corroborated by our electronic structure analysis which shows that the electronic band gap energy of the ambient temperature H4-like structure agrees much better with the experimentally reported band gap energies.</P> [FIG OMISSION]</BR>
Immediate effect of self-myofascial release on hamstring flexibility
( Jihye Jung ),( Wonjae Choi ),( Yonghyuk Lee ),( Jiwoo Kim ),( Hyunju Kim ),( Kyoungho Lee ),( Jaewoo Lee ),( Seungwon Lee ) 물리치료재활과학회 2017 Physical therapy rehabilitation science Vol.6 No.1
Objective: This study aimed to identify the area with greatest effect using self-myofascial release technique (self-MFR) in the hamstring, suboccipital, and plantar regions. Design: Cross-sectional study. Methods: Twenty-two adult subjects were evaluated for flexibility and hamstring pain threshold after self-MFR. Based on the superficial back line, the self-MFR application areas were the suboccipital region, hamstring, and plantar regions. Self-MFR was applied to each area using a wooden pole for a total of 4 minutes. Self-MFR was applied for 3 days at the same time of day, which was randomly assigned for each subject. Treatment was applied to one area each day. The sit and reach test (SRT), active range of motion (AROM), and passive ROM (PROM) were used to determine changes in flexibility, and an algometer was used to determine pain threshold. Pre/post-self-MFR effectiveness was tested using a paired t-test. Repeated measurement was used to compare self-MFR effects in the suboccipital, hamstring, and plantar regions. Results: When the self-MFR technique was applied to the 3 areas, the SRT showed significant improvement over baseline (p<0.05). Bilateral AROM and PROM showed significant improvements (p<0.05). When the self-MFR technique was applied to the hamstring, the semimembranosus showed a significant change in pain threshold (p<0.05). Conclusions: Our findings suggest that indirect application based on the Anatomy Trains could be effective for those who need to improve muscle flexibility. Moreover, self-MFR easily alleviates myofascial pain while maintaining flexibility, and can be performed at any time and place.
Immediate effect of self-myofascial release on hamstring flexibility
Jung, Jihye,Choi, Wonjae,Lee, Yonghyuk,Kim, Jiwoo,Kim, Hyunju,Lee, Kyoungho,Lee, Jaewoo,Lee, Seungwon korean Academy of Physical Therapy Rehabilitation 2017 Physical therapy rehabilitation science Vol.6 No.1
Objective: This study aimed to identify the area with greatest effect using self-myofascial release technique (self-MFR) in the hamstring, suboccipital, and plantar regions. Design: Cross-sectional study. Methods: Twenty-two adult subjects were evaluated for flexibility and hamstring pain threshold after self-MFR. Based on the superficial back line, the self-MFR application areas were the suboccipital region, hamstring, and plantar regions. Self-MFR was applied to each area using a wooden pole for a total of 4 minutes. Self-MFR was applied for 3 days at the same time of day, which was randomly assigned for each subject. Treatment was applied to one area each day. The sit and reach test (SRT), active range of motion (AROM), and passive ROM (PROM) were used to determine changes in flexibility, and an algometer was used to determine pain threshold. Pre/post-self-MFR effectiveness was tested using a paired t-test. Repeated measurement was used to compare self-MFR effects in the suboccipital, hamstring, and plantar regions. Results: When the self-MFR technique was applied to the 3 areas, the SRT showed significant improvement over baseline (p<0.05). Bilateral AROM and PROM showed significant improvements (p<0.05). When the self-MFR technique was applied to the hamstring, the semimembranosus showed a significant change in pain threshold (p<0.05). Conclusions: Our findings suggest that indirect application based on the Anatomy Trains could be effective for those who need to improve muscle flexibility. Moreover, self-MFR easily alleviates myofascial pain while maintaining flexibility, and can be performed at any time and place.
THE EFFECT OF OVER AND UNDERLAYER ON THE MAGNETORESISTANCE IN Co - Ag NANO - GRANULAR ALLOY FILMS
Yonghyuk Kim,Seong-Rae Lee 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.5
The composition and thickness dependence and the ferromagnetic under- and overlayer effect on the magnetoresistance ratio and saturation field of the Co-Ag nano-granular films were investigated. The maximum magnetoresistance (23% at R.T.) in the as-deposited state was obtained in the 3000Å Co_(30)Ag_(70) bare alloy film. As the thickness of the alloy films decreased below 500Å, the MR ratio decreased because of the resistivity increase and the non-uniform film formation. We showed that the ferromagnetic over- and underlayer could reduce the saturation field of the nano-granular films via exchange coupling effect. The magnetoresistance and the saturation field of the 100Å alloy film were 3.65 % and 2.85 kOe respectively and those of the under- and overlayered alloy films with 200Å Fe were 3.3 % and 1.23 kOe respectively.