Gravity model explained by the radiation model on a population landscape

Understanding the mechanisms behind human mobility patterns is crucial to improve our ability to optimize and predict traffic flows. Two representative mobility models, i.e., radiation and gravity models, have been extensively compared to each other against various empirical data sets, while their fundamental relation is far from being fully understood. In order to study such a relation, we first model the heterogeneous population landscape by generating a fractal geometry of sites and then by assigning to each site a population independently drawn from a power-law distribution. Then the radiation model on this population landscape, which we call the radiation-on-landscape (RoL) model, is compared to the gravity model to derive the distance exponent in the gravity model in terms of the properties of the population landscape, which is confirmed by the numerical simulations. Consequently, we provide a possible explanation for the origin of the distance exponent in terms of the properties of the heterogeneous population landscape, enabling us to better understand mobility patterns constrained by the travel distance.Comment: 14 pages, 4 figure

Spin polarization amplification within nonmagnetic semiconductors at room temperature

We demonstrate theoretically that the spin polarization of current can be electrically amplified within nonmagnetic semiconductors by exploiting the fact the spin current, compared to the charge current, is weakly perturbed by electric driving forces. As a specific example, we consider a T-shaped current branching geometry made entirely of a nonmagnetic semiconductor, where the current is injected into one of the branches (input branch) and splits into the other two branches (output branches). We show that when the input current has a moderate spin polarization, the spin polarization in one of the output branches can be higher than the spin polarization in the input branch and may reach 100% when the relative magnitudes of current-driving electric fields in the two output branches are properly tuned. The proposed amplification scheme does not use ferromagnets or magnetic fields, and does not require low temperature operation, providing an efficient way to generate a highly spin polarized current in nonmagnetic semiconductors at room temperature.Comment: 11 pages, 2 figures, to appear in Phys. Rev.

Current-Induced Magnetic Domain-Wall Motion by Spin Transfer Torque: Collective Coordinate Approach with Domain-Wall Width Variation

The spin transfer torque generated by a spin-polarized current can induce the shift of the magnetic domain-wall position. In this work, we study theoretically the current-induced domain-wall motion by using the collective coordinate approach [Gen Tatara and Hiroshi Kohno, Phys. Rev. Lett. 92, 86601 (2004)]. The approach is extended to include not only the domain-wall position and the polarization angle changes but also the domain-wall width variation. It is demonstrated that the width variation affects the critical current.Comment: 13 pages, 3 figure

Anti-aging activities of Pyrus pyrifolia var culta plant callus extract

Purpose: To investigate the anti-aging properties of callus extract from Pyrus pyrifolia var. culta with skin regeneration and lightening activities.Methods: Callus extract of P. pyrifolia var. culta was produced on Murashige and Skoog (MS) medium supplemented with picloram, followed by extraction of the callus biomass in phosphate-buffered saline. The anti-oxidant activity of the extract was assessed using the DPPH free radical-scavenging assay. Inhibition of skin pigmentation by callus extract was evaluated by measuring the melanogenesis of melanoma cells. The skin-regenerating efficacy of the extract was evaluated in terms of its ability to promote procollagen synthesis and fibroblast cell proliferation.Results: The callus extract, at 10 mg/mL, exhibited 78.7 % free radical-scavenging activity, equivalent to that exhibited by 500 μM ascorbic acid. The 1 mg/mL extract solution afforded a 1.4-fold greater reduction in melanocyte melanin than did a 1 mg/mL arbutin solution. Fibroblast cells treated with 5 mg/mL callus extract exhibited 127 % higher levels of proliferation and 2.0-fold higher levels of procollagen type I C-peptide synthesis, respectively, compared with the untreated controls.Conclusion: These findings suggest that the callus extract of P. pyrifolia var. culta may be useful as a source of anti-aging cosmetic components with skin lightening and regenerating activities.Keywords: P. pyrifolia var. culta, Anti-aging, Callus extract, Skin lightening, Anti-tyrosinase activity, Melanogenesis, Wound recovery, Procollagen type I C-peptide synthesi

Analysis of differences in variables related to health and safety according to the employment type of Korean workers

Introduction: The purpose of this study was to understand the differences in variables related to health and safety according to the employment type of Korean workers, specifically to identify the differences by employment type on in health status, the likelihood of wearing protective gear when working, access to manuals on emotional expression, and access to information on risk factors related to health and safety. Methods: The secondary data of four items on employment type, health type of workers and safety among the 5th Korean Working Condition Survey conducted in 2017 in Korea was used in this study. The data of workers were processed by using SPSS/WIN 23.0 Program and R 3.1.2, and demographic characteristics were quantified as frequency and percentage.  Results: A total of 30,300 employed people were surveyed. The result shows that part-time workers have poorer health than full-time workers (c2 = 540.7155, p < 0.05), insufficiently wore protective gear (c2 = 24.8702, p < 0.05), had insufficient access to manuals on emotional expression (c2 = 27.7612, p < 0.05) and lacked information about risk factors (c2 = 185.0082, p < 0.05). Conclusion: Health and safety manager will need to have education and consultation, development of manual and perform an early intervention to improve safety environment as primary health care providers by understanding factors related to health and safety of part-time workers

Multiple gravity laws for human mobility within cities

The gravity model of human mobility has successfully described the deterrence of travels with distance in urban mobility patterns. While a broad spectrum of deterrence was found across different cities, yet it is not empirically clear if movement patterns in a single city could also have a spectrum of distance exponents denoting a varying deterrence depending on the origin and destination regions in the city. By analyzing the travel data in the twelve most populated cities of the United States of America, we empirically find that the distance exponent governing the deterrence of travels significantly varies within a city depending on the traffic volumes of the origin and destination regions. Despite the diverse traffic landscape of the cities analyzed, a common pattern is observed for the distance exponents; the exponent value tends to be higher between regions with larger traffic volumes, while it tends to be lower between regions with smaller traffic volumes. This indicates that our method indeed reveals the hidden diversity of gravity laws that would be overlooked otherwise.Comment: 17 pages, 6 figure