2,040 research outputs found
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
A common trajectory recapitulated by urban economies
Is there a general economic pathway recapitulated by individual cities over
and over? Identifying such evolution structure, if any, would inform models for
the assessment, maintenance, and forecasting of urban sustainability and
economic success as a quantitative baseline. This premise seems to contradict
the existing body of empirical evidences for path-dependent growth shaping the
unique history of individual cities. And yet, recent empirical evidences and
theoretical models have amounted to the universal patterns, mostly
size-dependent, thereby expressing many of urban quantities as a set of simple
scaling laws. Here, we provide a mathematical framework to integrate repeated
cross-sectional data, each of which freezes in time dimension, into a frame of
reference for longitudinal evolution of individual cities in time. Using data
of over 100 millions employment in thousand business categories between 1998
and 2013, we decompose each city's evolution into a pre-factor and relative
changes to eliminate national and global effects. In this way, we show the
longitudinal dynamics of individual cities recapitulate the observed
cross-sectional regularity. Larger cities are not only scaled-up versions of
their smaller peers but also of their past. In addition, our model shows that
both specialization and diversification are attributed to the distribution of
industry's scaling exponents, resulting a critical population of 1.2 million at
which a city makes an industrial transition into innovative economies
A house price valuation based on the random forest approach: the mass appraisal of residential property in South Korea
Mass appraisal is the standardized procedure of valuing a large number of properties at the same time and is commonly used to compute real estate tax. While a hedonic pricing model based on the ordinary least squares (OLS) linear regression has been employed as the traditional method in this process, the stability and accuracy of the model remain questionable. This paper investigates the features of a house price predictor based on the Random Forest (RF) method by comparing it with that of a conventional hedonic pricing model. We used apartment transaction data from the period of 2006 to 2017 in the district of Gangnam, one of the most developed areas in South Korea. Using a data set covering 40% of all transactions in the sample area, we demonstrate that the accuracy of a machine learning-based predictor can be surprisingly high. The average of percentage deviations between the predicted and the actual market price was found to be only around 5.5% in the RF predictor, whereas it was almost 20% in the OLS-based predictor. With the RF predictor, the probability of the predicted price being within 5% of its actual market price was 72%, while only about 17.5% of the regression-based predictions fell within the same range. These results show that, in the practice of mass appraisal, the RF method may be a useful complement to the hedonic models, as it more adequately captures the complexity or non-linearity of actual housing markets.
First published online 03 February 202
Measuring national capability over big science's multidisciplinarity: A case study of nuclear fusion research
In the era of big science, countries allocate big research and development budgets to large scientific facilities that boost collaboration and research capability. A nuclear fusion device called the "tokamak" is a source of great interest for many countries because it ideally generates sustainable energy expected to solve the energy crisis in the future. Here, to explore the scientific effects of tokamaks, we map a country's research capability in nuclear fusion research with normalized revealed comparative advantage on five topical clusters-material, plasma, device, diagnostics, and simulation-detected through a dynamic topic model. Our approach captures not only the growth of China, India, and the Republic of Korea but also the decline of Canada, Japan, Sweden, and the Netherlands. Time points of their rise and fall are related to tokamak operation, highlighting the importance of large facilities in big science. The gravity model points out that two countries collaborate less in device, diagnostics, and plasma research if they have comparative advantages in different topics. This relation is a unique feature of nuclear fusion compared to other science fields. Our results can be used and extended when building national policies for big science.11Yscopu
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
Importance of remission and residual somatic symptoms in health-related quality of life among outpatients with major depressive disorder: a cross-sectional study
Background: Major depressive disorder (MDD) is strongly associated with an impaired quality of life (QoL), which is itself affected by various factors. Symptom-oriented ratings poorly reflect the impact of disease on the QoL and level of functioning of the mental health of subjects. The purpose of this study was to assess health-related QoL (HRQoL) using preference-based measures in outpatients with MDD with regard to their remission achievement and clinical factors affecting the HRQoL. Methods: This was a cross-sectional observational study. We recruited 811 patients with MDD from 14 psychiatric outpatient clinics in Korea. They were divided into three groups as follows: a new visit group (n = 287), a remitted group (n = 235), and a non-remitted group (n = 289). The 17-item Hamilton Depression Rating Scale was used to assign patients to the remitted or non-remitted group. The general HRQoL was assessed with the EuroQol 5D (EQ-5D), using both the EQ-5D index score and the EuroQol Visual Analog Scale (EQ-VAS). The disease-specific HRQoL was assessed with the Quality of Life Enjoyment and Satisfaction Questionnaire Short Form (Q-LES-Q-SF). Results: The non-remitted group showed a significant impairment of HRQoL in view of the subscales of EQ-5D index scores, EQ-VAS, and Q-LES-Q-SF. The EQ-5D index score in the remitted group was 0.77 ± 0.10, while it was 0.57 ± 0.23 in the non-remitted group and 0.58 ± 0.24 in the new visit group (p < 0.0001). The EQ-VAS scores for the remitted and non-remitted groups were 72.5 ± 16.6 and 50.9 ± 20.3, respectively (p < 0.0001). Likewise, patients with remission had the Q-LES-Q-SF total score of 46.5 ± 8.8, whereas those with non-remission reported 36.7 ± 7.7 (p < 0.0001). The symptom severity measured by the Depression and Somatic Symptoms Scale was significantly correlated with the HRQoL. Furthermore, patients with severe somatic symptoms showed a significantly lower EQ-5D index score (0.54 ± 0.24) than those with mild/moderate somatic symptoms (0.75 ± 0.12; p = 0.002). Conclusion: Non-remitted MDD patients, especially those with more severe somatic symptoms, show a distinct impairment of HRQoL and more clinical symptoms, suggesting the importance of achieving remission in the treatment of MDD
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