Study on the Evolution of the Source-Flow-Sink Pattern of China’s Chunyun Population Migration Network: Evidence from Tencent Big Data

We construct a comprehensive analysis framework of population flow in China. To do so, we take prefecture-level administrative regions as the basic research unit of population flow and use source-sink theory and flow space theory. Additionally, we reveal the dynamic differentiation of population flow patterns and the evolution of population source-flow-sink systems. We try to provide a theoretical basis for the formulation of population development policies and regional spatial governance. The results show the following: (1) The Hu Huanyong Line has a strong spatial lock-in effect on population flow. Additionally, provincial capital cities, headed by Hangzhou, Nanjing, and Hefei, have played an increasingly prominent role in population flow. (2) The developed eastern coastal areas have undertaken China’s main population outflow. The net population flow is spatially high in the middle of the region and low on the two sides, exhibiting an “inverted U-shaped” pattern. Furthermore, the borders of the central provinces form a continuous population inflow area. (3) The hierarchical characteristics of the population flow network are obvious. Strong connections occur between developed cities, and the effect of distance attenuation is weakened. The medium connection network is consistent with the traffic skeleton, and population flow exhibits a strong “bypass effect”. (4) The source and sink areas are divided into four regions similar to China’s three major economic belts. The 10 regions can be refined to identify the main population source and sink regions, and the 18 regions can basically reflect China’s level of urbanization. The network of the population flow source-flow-sink system exhibits notable nesting characteristics. As a result, it creates a situation in which the source areas on both sides of the east and the west are convective to the middle. The hierarchical differentiation of the source-flow sink system is related to the differences between the east and the west and between the north and the south, as well as local differences in China.

Study on the Spatial Pattern of Migration Population in Egypt and Its Flow Field Characteristics from the Perspective of “Source-Flow-Sink”

Based on the provinces as the spatial nodes of population migration, a “Source-Flow-Sink” analysis framework of population migration flow in Egypt was established by “Source-Sink” Theory and Flow Field Theory to study the migration population in Egypt. It reveals the spatial pattern of the migration population in Egypt and its flow field characteristics and provides theoretical basis for the formulation of population development policies and regional spatial governance planning. The results show that: (1) there are significant spatial differences in the size and rate of migration in Egypt. In 2017, the migration population in Egypt exceeded 2.2 million in total, with a migration rate of 2.33%, and the extreme multiple reached 80 and 12. (2) According to the spatial pattern of geographical distribution, the Source System is divided into five types: axis type, layer type, fan type, oblique symmetry type, and scattered jump type. There are only three types in Sink System, namely wide area coverage type, local development type, and scattered jump type. Source Places lie in the middle, Sink Places are symmetrical from east to west, and Exchange Places are concentrated along the Mediterranean coast in the north of Cairo on the whole, with the initial formation of a “core-periphery” spatial pattern. (3) The interprovincial population migration flow in Egypt is dominated by neighborhood penetration and polarization of high-rank nodes (capitals or regional economic centers), giving rise to 7 modes of central system spatial structures and 3 modes of pole-core interaction. The central system of flow fields with clear priorities and the streamline channel network with layered trunks and branches basically take shape, overall characterized by stepped runoff from east to west, and local convection from south to north.

Source Flow in Heterogeneous Aquifers with Application to Hydraulic Tomography

<p>Enhanced spreading of contaminants by groundwater (macrodispersion) is governed by advection by the velocity field, whose spatial variability is caused by the heterogeneity of the hydraulic conductivity K. Characterization of K distribution in space is a major topic of research. While considerable knowledge has been accumulated for natural gradient flows, hydraulic tomography methods have been forwarded only recently. A typical setup consists of short segments of a well through which water is pumped (injected) and the head H response is measured by pressure transducers along observation piezometers at different distances and elevations. Attempts in the past were done mainly to derive K from measured H  by numerical inversion of the flow equation accordingly to a global optimality condition. The present study considers stochastic hydraulic tomography by which measured H are employed in order to identify the statistical parameters of the log-conductivity Y= ln K field (mean, variance, integral scales). As a first step we investigate and present the solution of the steady flow equations relating  H statistical moments to those of the K field for the strongly nonuniform source flow, which approximates the main constitutive element of the tomographic setup. This is achieved by numerical simulations for values of the Y variance up to 4 and the derivation of type curves which helps in the identification of K statistics. Application to identification of logconductivity moments for a hydraulic tomography setup is illustrated by a synthetic example.</p>

Method Development and Validation For Determining Stability of Omadacycline In Biological Matrices By Liquid Chromatography–Mass Spectrometry

The validated protein precipitation method was applied for the estimation of Omadacycline (OM) in human plasma with Omadacycline-D9 (OMD9) as an internal standard (ISTD) by using HPLC-ESI-MS/MS. Zorbax Eclipse Plus C18, 2.1 x 50 mm, 3.5 μm, was selected as the analytical column. The column temperature was set at 45°C. Mobile phase composition was 0.1% formic acid: methanol (80:20 v/v). Source flow rate of 300 μL/min without a split. An injection volume of 10 μL. Omadacycline and Omadacycline-D9 mesylate were eluted at 1.2 ± 0.2 min, with a total run time of 3.0 min for each sample. The mass transitions of Omadacycline and Omadacycline-D9 obtained were m/z 557.6 ® 456.6 and 566.7 ® 456.6, respectively. The standard curve shows a correlation coefficient (r2) greater than 0.9983 with a range of 5.00 to 12000.00 pg/ml using the linear regression model.