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This empirical study shows how people use their smartphones by employing the rational addiction model of Becker and Murphy. The analysis uses micro-level panel data on the monthly usage of smartphone applications (so-called “apps”) derived from 10,337 users in South Korea, from 2012 to 2016. The authors find that smartphone users are “addicted” to mobile phone apps, in the sense that their prior usage has significantly influenced their current use. Nonetheless, people in the sample seem to use their smartphones in a forward-looking manner, adjusting consumption over time to maximize their utility. On the other hand, the study's result rejects the conventional belief that younger individuals behave more myopically than older ones. Furthermore, only the mother's smartphone use was found to generate a positive externality for her children.

In ultrasound color Doppler imaging(CDI), effective clutter rejection is essential for estimating flow velocity and power. Since the clutter has time-varying characteristics, it is challenging to suppress it with a static clutter filter. In this paper, a new adaptive clutter rejection method based on spectral decomposition and tissue acceleration (ACR) for suppressing nonstationary clutter is presented. In the proposed method, tissue and flow characteristics are analyzed from singular value decomposition of backscattered Doppler signals to select optimal clutter filter from a bank of clutter filters. To evaluate the ACR method, phantom and in vivo experiments were conducted. For the phantom experiments, 20 frames of complex baseband data were acquired with a commercial ultrasound system (V10, Samsung Medison, Seoul, Korea) using a 3.5-MHz convex array probe by tapping over the flow phantom (Gammex 1425A LE, Gammex, Middleton, WI, USA) surface to mimic tissue movements. Similarly, 20 frames of in vivo liver data from a volunteer were also acquired. The performance of the proposed ACR method was compared with conventional clutter rejection methods, i.e., static (ST) and down-mixing (DM), using a commonly-used flow signal-to-clutter ratio (SCR) and fractional residual clutter area (FRCA). From the phantom experiments, the ACR method provided 2.03 dB and 0.98 dB improvements in SCR over the ST and DM methods. Similarly, ACR showed improvements in fractional residual clutter area (FRCA) compared to the ST and DM methods (i.e., 2.3% vs. 5.4 % and 3.7%, respectively). The consistent results were obtained with the in vivo experiments. The improvement in SCR from the ACR method is 4.90 dB and 3.98 dB, compared to the ST and DM methods. In addition, the ACR method showed less than 1% FRCA values for all 20 frames of in vivo data. These results indicate that the proposed ACR based on spectral decomposition and tissue acceleration can improve image quality in ultrasound color Doppler imaging by effectively removing the clutter.

The root ofOstericum koreanumMaximowicz has been used as a traditional medicine called “Kanghwal” in Korea (or “Qianghuo” in China). The purpose of this study was to investigate the vasorelaxant activity and mechanism of action of an ethanol extract of theO. koreanumroot (EOK). We used isolated rat aortic rings to assess the effects of EOK on various vasorelaxant or vasoconstriction factors. EOK induced vasorelaxation in phenylephrine hydrochloride (PE) or KCl precontracted aortic rings in a concentration-dependent manner. However, the vasorelaxant effects of EOK on endothelium-intact aortic rings were reduced by pretreatment withL-NAME or methylene blue. In Ca2+-free Krebs-Henseleit solution, pretreatment with EOK (0.3 mg/mL) completely inhibited PE-induced constriction. In addition, EOK (0.3 mg/mL) also completely inhibited vasoconstriction induced by supplemental Ca2+in aortic rings that were precontracted with PE or KCl. Furthermore, the EOK-induced vasorelaxation in PE-contracted aortic rings was inhibited by preincubation with nifedipine. These results indicate that the vasorelaxant effects of EOK are responsible for the induction of NO formation fromL-Arg and NO-cGMP pathways, blockage of the extracellular Ca2+entry via the receptor-operative Ca2+channel and voltage-dependent calcium channel, and blockage of sarcoplasmic reticulum Ca2+release via the inositol triphosphate pathway.