Low-dimensional heat conduction in surface phonon polariton waveguide.

Heat conduction in solids is typically governed by the Fourier's law describing a diffusion process due to the short wavelength and mean free path for phonons and electrons. Surface phonon polaritons couple thermal photons and optical phonons at the surface of polar dielectrics, possessing much longer wavelength and propagation length, representing an excellent candidate to support extraordinary heat transfer. Here, we realize clear observation of thermal conductivity mediated by surface phonon polaritons in SiO2 nanoribbon waveguides of 20-50 nm thick and 1-10 µm wide and also show non-Fourier behavior in over 50-100 µm distance at room and high temperature. This is enabled by rational design of the waveguide to control the mode size of the surface phonon polaritons and its efficient coupling to thermal reservoirs. Our work laid the foundation for manipulating heat conduction beyond the traditional limit via surface phonon polaritons waves in solids.

A study on the relationships between playfulness, physical self-efficacy, and school happiness among middle school students participating in "0th-period physical education class" in South Korea.

The purpose of this study is to create a scientific basis for the establishment of "0th-period physical education class" activities in schools in the future, with the expectation that the associations of morning exercise can be activated in the Korean educational community. To achieve this goal, the present study aimed to determine the relationship between the playfulness experienced during the early morning exercise of middle school students and their physical self-efficacy and education for happiness. To examine the model, questionnaires were collected from 296 middle school students located in Seoul and Gyeonggi-do, South Korea. Correlation analysis and standard multiple regression analysis were performed to analyze the data using the SPSS 21.0. The findings were as follows: First, the playfulness of the middle school "0th-period physical education class" had a significant effect on physical self-efficacy. Second, playfulness had a significant effect on education for happiness. Thirdly, physical self-efficacy was found to have a significant effect on education for happiness. Based on the results of this study, we suggest that a "0th-period physical education class" with various activities should be held during the legally required time in South Korea.

Relationship between perceived enjoyment, exercise commitment and behavioral intention among adolescents participating in "School Sport Club".

This study aimed to examine ways to improve the quality of physical activity (PA) to address social problems related to obesity and being overweight among adolescents, through an educational approach. In this regard, the current study identified associations between factors that lead to sustained PA participation among middle school students participating in school sports club activities, and derived academic implications that can be incorporated into future school education programs. The researchers explored the relationship between perceived enjoyment, exercise commitment, and behavioral intention in middle school sports club participants. The subjects of the study were selected as middle school students who had participated in school sports clubs for more than 6 months. Using convenience sampling, 350 datasets were collected from middle school students living in metropolitan cities in South Korea. Finally, 336 datasets were used for the final analysis after eliminating 14 questionnaires that were judged to be incorrectly indicated or incomplete. Frequency analysis, exploratory factor analysis, and reliability verification (Cronbach's α) were conducted. The findings were as follows: first, among the sub-factors of perceived enjoyment, the following were found to have a positive relationship with cognitive commitment: daily escape (ß = 0.259), competitive victory (ß = 0.228), interpersonal relationships (ß = 0.204), and physical fitness (ß = 0.119). Furthermore, among the sub-factors of perceived fun, physical health (ß = 0.330), daily escape (ß = 0.205), interpersonal relationships (ß = 0.307), and competitive victory (ß = 0.228) had positive relationships with behavioral commitment. Second, among the sub-factors of perceived enjoyment, physical health (ß = 0.423), interpersonal relations (ß = 0.139), and daily escape (ß = 0.138) were found to have a positive association with behavioral intention. On the other hand, there was no significant relationship between competitive winning (ß = 0.071) and behavioral intention. Third, behavioral commitment (ß = 0.237) and cognitive commitment (ß = 0.183) were confirmed to have a significant positive relationship with behavioral intention. These findings highlight that middle school students' perceived enjoyment from participating in school sports clubs is a positive factor leading to increased immersion in sports activities and a sufficient basis for continuing sports activities. Furthermore, class organization, environmental factors, and appropriate instructional content for school sports club activities are essential for exercise commitment.

A Study on the Subjectivity of Parents Regarding "0th-Period Physical Education Class" of Middle Schools in Korea Using Q-Methodology.

The current study examined parents' subjective perception types and characteristics regarding the 0th-Period Physical Education Class of Middle School in Korea. The Q-methodology was applied, and the final 25 Q-Samples were selected through the composition of the 42 Q-population. Among Korean parents, 20 students who participated in "Physical Education Activities in Class 0" for more than one year were selected as P-Sample. Q-sorting was performed by the P-Sample. Data collected by Q-sorting were analyzed using the PQ method program version 2.35, with centroid factor analysis and varimax rotation. The finding pointed to four types, with a total explanatory variance of 63%. Type 1 (N = 7), and was named "urgent legal and institutional settlement of 0th-period physical education". Type 2 (N = 4) has the theme of "beach-head for a vibrant school life". Type 3 (N = 4) was named "enhancement of academic capability". Type 4 (N = 4) was described as "strengthening physical and mental health". Moreover, the consensus statements between each type were investigated in Q1 and Q2. These findings highlight the importance of the "0th-period physical education class" so the program could be expanded and institutionalized in Korea.

Subjective Perceptions of South Korean Parents Regarding the Effectiveness of Taekwondo Education for Adolescents and Its Characteristics: The Q Methodology Application.

This study aims to determine why Korean parents provide adolescent children with continuous physical education through Taekwondo. The Q methodology was applied. The final 25 Q-samples were selected by composing the Q-population. Twenty parents who provided their children with Taekwondo education for more than 10 years were designated as the P-sample. Q-sorting was performed on the P-sample. Centroid factor analysis and varimax rotation were performed using version 2.35 of PQ method program. The study observed four factors with a total explanatory variance of 69%. Types 1 to 4 (N = 5, 7, 5, and 3) pertained to a powerful means of enhancing mental health, the driving force behind stable school life and social development, improvement in psychological and social areas for a successful transition to adulthood, and increased awareness of the values of Taekwondo and importance of physical activity, with eigenvalues of 4.59, 6.42, 3.16, and 1.18 and explanatory variances of 0.16, 0.32, 0.12, and 0.09, respectively. Furthermore, consensus statements for each type were investigated as Q18 and Q17. These findings supported the academic foundation of proper Taekwondo education in adolescence and confirmed it as a powerful means of exerting a positive impact on adulthood.

Causal Model of Participation, Perceived Enjoyment, and Learning Attitudes in "the 0th Period Physical Education Class" of Middle Schools in South Korea.

This study aims to establish the basis for the institutional implementation of the 0th period physical education class to promote the health and academic performance of Korean teenagers. To achieve this goal, this study determined the impact of middle school students' participation in physical activities during the 0th period on perceived enjoyment and learning attitude. To examine the model, 282 questionnaires were collected from middle school students in a metropolitan city in South Korea. The samples were obtained using the convenience sampling method, and correlation analysis and structural equation modeling were performed using SPSS 21.0 and Amos 21.0. The findings are as follows: first, the participation of middle school students in physical activities during the 0th period had a statistically significant effect on perceived enjoyment. Second, perceived enjoyment had no statistically significant effect on learning attitude. Third, participation was shown to have a significant effect on learning attitudes. These findings supported the academic basis for the implementation of the 0th period physical education class for middle school students and application of practical measures to encourage their participation.

Intertube Aggregation-Dependent Convective Heat Transfer in Vertically Aligned Carbon Nanotube Channels.

The heat transfer of carbon nanotube fin geometry has received considerable attention. However, the flow typically occurred over or around the pillars of nanotubes due to the greater flow resistance between the tubes. Here, we investigated the forced convective heat transfer of water through the interstitial space of vertically aligned multiwalled carbon nanotubes (VAMWNTs, intertube distance = 69 nm). The water flow provided significantly a greater Reynolds number (Re) and Nusselt number (Nu) than air flow due to the greater density, heat capacity, and thermal conductivity. However, it resulted in surface tension-induced nanotube aggregation after the flow and drying process, generating random voids in the nanotube channel. This increased permeability (1.27 × 10-11 m2) and Re (2.83 × 10-1) but decreased the heat transfer coefficient (h, 9900 W m-2 K-1) and Nu (53.77), demonstrating a trade-off relationship. The h (25,927 W m-2 K-1) and Nu (153.49) could be further increased, at an equivalent permeability or Re, by increasing nanotube areal density from 2.08 × 1010 to 1.04 × 1011 cm-2. The area-normalized thermal resistance of the densified and aggregated VAMWNTs was smaller than those of the Ni foam, Si microchannel, and carbon nanotube fin array, demonstrating excellent heat transfer characteristics.

Fast mass transport-assisted convective heat transfer through a multi-walled carbon nanotube array.

The recently reported fast mass transport through nanochannels provides a unique opportunity to explore nanoscale energy transport. Here we experimentally investigated the convective heat transport of air through vertically aligned multi-walled carbon nanotubes (VAMWNTs). The flow through the unit cell, defined as an interstitial space among four adjacent nanotubes (hydraulic diameter = 84.9 nm), was in the transition (0.62 ≤ Knudsen number ≤ 0.78) and creeping flow (3.83 × 10-5 ≤ Reynolds number (Re) ≤ 1.55 × 10-4) regime. The constant heat flux (0.102 or 0.286 W m-2) was supplied by a single-mode microwave (2.45 GHz) instantly heating the VAMWNTs. The volume flow rate was two orders of magnitude greater than the Hagen-Poiseuille theory value. The experimentally determined convective heat transfer coefficient (h, 3.70 × 10-4-4.01 × 10-3 W m-2 K-1) and Nusselt number (Nu, 1.17 × 10-9-1.26 × 10-8) were small partly due to the small Re. A further increase in Re (2.12 × 10-3) with the support of a polytetrafluoroethylene mesh significantly increased h (5.48 × 10-2 W m-2 K-1) and Nu (2.37 × 10-7). A large number of nanochannels in a given cross-section of heat sinks may enhance the heat dissipation significantly.

Enhanced water vapor separation by temperature-controlled aligned-multiwalled carbon nanotube membranes.

Here we present a new strategy of selectively rejecting water vapor while allowing fast transport of dry gases using temperature-controlled aligned-multiwalled carbon nanotubes (aligned-MWNTs). The mechanism is based on the water vapor condensation at the entry region of nanotubes followed by removing aggregated water droplets at the tip of the superhydrophobic aligned-MWNTs. The first condensation step could be dramatically enhanced by decreasing the nanotube temperature. The permeate-side relative humidity was as low as ∼17% and the helium-water vapor separation factor was as high as 4.62 when a helium-water vapor mixture with a relative humidity of 100% was supplied to the aligned-MWNTs. The flow through the interstitial space of the aligned-MWNTs allowed the permeability of single dry gases an order of magnitude higher than the Knudsen prediction regardless of membrane temperature. The water vapor separation performance of hydrophobic polytetrafluoroethylene membranes could also be significantly enhanced at low temperatures. This work combines the membrane-based separation technology with temperature control to enhance water vapor separation performance.

Reverse capillary flow of condensed water through aligned multiwalled carbon nanotubes.

Molecular transport through nanopores has recently received considerable attention as a result of advances in nanofabrication and nanomaterial synthesis technologies. Surprisingly, water transport investigations through carbon nanochannels resulted in two contradicting observations: extremely fast transport or rejection of water molecules. In this paper, we elucidate the mechanism of impeded water vapor transport through the interstitial space of aligned multiwalled carbon nanotubes (aligned-MWCNTs)--capillary condensation, agglomeration, reverse capillary flow, and removal by superhydrophobicity at the tip of the nanotubes. The origin of separation comes from the water's phase change from gas to liquid, followed by reverse capillary flow. First, the saturation water vapor pressure is decreased in a confined space, which is favorable for the phase change of incoming water vapor into liquid drops. Once continuous water meniscus is formed between the nanotubes by the adsoprtion and agglomeration of water molecules, a high reverse Laplace pressure is induced in the mushroom-shaped liquid meniscus at the entry region of the aligned-MWCNTs. The reverse Laplace pressure can be significantly enhanced by decreasing the pore size. Finally, the droplets pushed backward by the reverse Laplace pressure can be removed by superhydrophobicity at the tip of the aligned-MWCNTs. The analytical analysis was also supported by experiments carried out using 4 mm-long aligned-MWCNTs with different intertube distances. The water rejection rate and the separation factor increased as the intertube distance decreased, resulting in 90% and 10, respectively, at an intertube distance of 4 nm. This mechanism and nanotube membrane may be useful for energy-efficient water vapor separation and dehumidification.

Enhanced condensation, agglomeration, and rejection of water vapor by superhydrophobic aligned multiwalled carbon nanotube membranes.

The separation of gas molecules and water vapor has become increasingly important for electronic, energy, and environmental systems. Here we demonstrate a new mechanism of enhanced condensation, agglomeration, and rejection of water vapor by superhydrophobic aligned multiwalled carbon nanotubes with the intertube distance of 73 nm, channel aspect ratio of ~5.5 × 10(4), and tortuosity of 1.157. The array with the characteristic channel dimension some 300 times greater than the target molecule size effectively suppressed water molecular transport at room temperature with the selectivity as high as ~2 × 10(5) (H(2)/H(2)O). The flow through the interstitial space of nanotubes allowed high permeability of other gas molecules (2.1 × 10(-9) to 3.8 × 10(-8) mol · m/m(2) · s · Pa), while retaining high selectivity, which is orders of magnitude greater than the permeate flux of polymeric membranes used for the water-gas mixture separation. This new separation mechanism with high selectivity and permeate flux, enabled by the unique geometry of aligned nanotubes, can provide a low-energy and cost-effective method to control humidity.