Development of a Refrigerant Distribution Header Applied to Microchannel Heat Exchangers

A microchannel heat exchanger applied to air conditioners has advantages because of its high heat transfer performance. However, there are some challenges to utilize its maximum performance. One of the most important challenges is refrigerant maldistribution resulting in heat transfer deterioration when it is used as an evaporator. The authors proposed a refrigerant distribution header that can be applied to variable capacity air conditioners, named “Refrigerant loop header.” In this paper, the “Refrigerant loop header”, which enables to equally distribute in a wide range of capacity, is introduced. In addition, high distribution performance is experimentally confirmed at different refrigerant mass flow rates

Antioxidative copper sinter bonding under thermal aging utilizing reduction of cuprous oxide nanoparticles by polyethylene glycol

Durability of sintered Cu joints under thermal aging in the air was investigated for the reduction of Cu₂O using Cu₂O/polyethylene glycol (PEG) mixture. Thermal analysis of the Cu₂O/PEG paste showed that the molecular weight of PEG influences the redox reaction and the subsequent bonding related to the combustion of the reducing organic solvent. Sintered Cu joints using PEG 400 exhibited high joint strength (above 30 MPa) in shear tests, even for the bonding temperature of 280 °C. The sintered Cu joints exhibited slightly increased strength during thermal aging at 250 °C in air, which was also confirmed by the microscale tensile test used for evaluating the fracture behavior of the sintered Cu structure. Microstructural analysis, including the evaluation of the crystal orientation, revealed a small change in the microstructure of sintered joints during aging. Transmission electron microscopy revealed the presence of organic membranes on slightly oxidized sintered Cu grains before thermal aging, and additional oxidation was observed after thermal aging. The progress of sintering during thermal aging in vacuum was different than that in air. It was considered that the formation of a thin Cu₂O layer, controlled by the presence of organic membranes, contributed to the suppression of Cu sintering.The version of record of this article, first published in Journal of Materials Science, is available online at Publisher’s website: https://doi.org/10.1007/s10853-023-08976-

A Keck/DEIMOS Spectroscopy of Lyman Alpha Blobs at Redshift z=3.1

We present the results of an intermediate resolution (~2 angstrom) spectroscopy of a sample of 37 candidate Lyman alpha blobs and emitters at redshift z=3.1 using the DEIMOS spectrograph on the 10 m Keck telescope. The emission lines are detected for all the 37 objects and have variety in their line profiles. The Lyman alpha velocity widths (FWHM) of the 28 objects with higher quality spectra, measured by fitting a single Gaussian profile, are in the range of 150 - 1700 km/s and correlate with the Lyman alpha spatial extents. All the 12 Lyman alpha blobs (>16 arcsec^2) have large velocity widths of > 500 km/s. While there are several possible physical interpretations of the Lyman alpha velocity widths (motion of gravitationally-bound gas clouds, inflows, merging of clumps, or outflows from superwinds), the large velocity widths of the Lyman alpha blobs suggest that they are the sites of massive galaxy formation. If we assume gravitationally-bound gas clouds, the dynamical masses of the Lyman alpha blobs are estimated to be ~10^12 - 10^13 Msun. Even for the case of outflows, the outflow velocities are likely to be the same order of the rotation velocities as inferred from the observational evidence for local starburst galaxies.Comment: Accepted for publication in ApJ

Development of a system for the assessment of a dual-task performance based on a motion-capture device

The authors produced a dual task (DT) that provided a dynamic balance task and a cognitive task in a game system using motion sensors and virtual images. There had been no DT where a cognitive task needs a dynamic balance task that requires full-body motions. We developed and evaluated a game system to assess the performance of the DT. The DT was to solve a Sudoku puzzle using full-body motions like Tái Chi. An ability to perform a DT is intimately related to risk of falls. To evaluate the developed system, we compared the performance of elderly people and young people. Generally, elderly people are at a higher risk of falls. Twenty elderly community-dwelling adults (mean age, 73.0±6.2 years) and 16 young adults (mean age, 21.8±1.0 years) participated in this study. To compare the two groups, we applied an independent-samples t-test. The time taken for the elderly people was 60.6±43.2 s, whereas the time taken for the young people was 16.0±4.8 s. The difference is statistically significant (p<0.05). This result suggests that the developed game system is useful for the evaluation of the DT performance

Differential determinants of physical daily activities in frail and nonfrail community-dwelling older adults

AbstractBackground/PurposeThe purpose of this study was to determine whether or not daily activities determined by average daily steps are associated with age, gender, body mass index, fear of falling, and physical functions (locomotive function, balance function, and muscle power) in community-dwelling nonfrail and frail older adults.MethodsThis is a cross-sectional study conducted in community-dwelling older adults in Japan. Based on the Timed Up and Go (TUG) test, 629 elderly adults were divided into two groups: 515 were grouped to nonfrail elderly (TUG time less than 13.5 seconds, mean age 77.0±7.2 years) and 114 to frail elderly (TUG time of 13.5 seconds or more, mean age 76.1±7.5 years). Daily physical activities were determined by average daily steps measured by pedometer and four other physical function tests (10-m walk test, single-leg standing, functional reach, and five-chair stand test) were performed along with the assessment of fear of falling.ResultsStepwise regression analysis revealed that age, gender, 10-m walk test, and single-leg standing were significant and independent determinants of the average step counts in the nonfrail elderly (R2=0.282, p<0.001), whereas fear of falling was the only significant and independent determinant of the average step counts in the frail elderly (R2=0.119, p<0.001).ConclusionThese results indicate that differential factors may be related to daily activities depending on the level of frailty in community-dwelling older adults