Despite the unique characteristics of urban forests, the motivating factors of urban forest visitors have not been clearly differentiated from other types of the forest resource. This study aims to identify the motivating factors of urban forest visitors, using latent Dirichlet allocation (LDA) topic modeling based on social big data. A total of 57,449 cases of social text data from social blogs containing the keyword “urban forest” were collected from Naver and Daum, the major search engines in South Korea. Then, 17,229 cases were excluded using morpheme analysis and stop word elimination; 40,110 cases were analyzed to identify the motivating factors of urban forest visitors through LDA topic modeling. Seven motivating factors—“Cafe-related Walk”, “Healing Trip”, “Daily Leisure”, “Family Trip”, “Wonderful View”, “Clean Space”, and “Exhibition and Photography”—were extracted; each contained five keywords. This study elucidates the role of forests as a place for healing, leisure, and daily exercise. The results suggest that efforts should be made toward developing various programs regarding the basic functionality of urban forests as a natural resource and a unique place to support a diversity of leisure and cultural activities.

Cryopreservation, which is one of assisted reproductive technologies, is developed to improve limited conservation period of liquid preservation of mammalian spermatozoa (Yoshida, 2000), and it facilitates preservation of sperm from superior individuals, prevention of contamination by virus, and selective production of individuals. Despite advantages of cryopreservation, efficiency of this technique is still low because spermatozoa are exposed to damages

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Republic of KoreaORCID (for more information, please visit https://orcid.org) Jihwan Lee (http://orcid.org/0000-0002-0040-3104) Inchul Choi (https://orcid.org/0000-0001-5011-2658) Competing interestsNo potential conflict of interest relevant to this article was reported. Funding sourcesState funding sources (grants, funding sources, equipment, and supplies). Include name and number of grant if available.

For the various next generation flexible devices such as wearable devices, implantable devices, etc., adhesion strength between different surfaces is very important for the reliable operation of the devices. In this study, to improve the adhesion strength between metal (Cu) and polymer substrate (prepreg), a plasma press process, where two surfaces are hot pressed together while generating a plasma between them, were used and the effect of plasma press method on the adhesion strength between prepreg and Cu were investigated and the results were compared with a conventional hot press method. When the prepreg surface was treated with a plasma using He/N 2 /O 2 or He/O 2 before hot press, the adhesion strength was decreased compared to the hot press without previous plasma treatment due to the hardening of the prepreg surface before the hot press. In contrast, when the Cu surface was treated with a plasma using He/N 2 /O 2 or He/O 2 before hot press, the adhesion strength was increased about 20% compared to the hot press only due to the formation hydroxyl group and Cu 2+ on the Cu surface before the hot press. However, when the prepreg and Cu were plasma pressed together, the use of He/O 2 and He/N 2 /O 2 improved the adhesion strength significantly about 35% and 75%, respectively, compared to the hot press only due to the activation of the prepreg surface and Cu surface during the hot press by forming dangling bonds on the surfaces in addition to the formation of hydroxyl group and oxygen bonding on the surfaces.