Stochastic P-bifurcation in a tri-stable Van der Pol system with fractional derivative under Gaussian white noise

In this paper, we study the tri-stable stochastic P-bifurcation problem of a generalized Van der Pol system with fractional derivative under Gaussian white noise excitation. Firstly, using the principle for minimal mean square error, we show that the fractional derivative term is equivalent to a linear combination of the damping force and restoring force, so that the original system can be transformed into an equivalent integer order system. Secondly, we obtain the stationary Probability Density Function (PDF) of the system’s amplitude by the stochastic averaging, and using the singularity theory, we find the critical parametric conditions for stochastic P-bifurcation of amplitude of the system, which can make the system switch among the three steady states. Finally, we analyze different types of the stationary PDF curves of the system amplitude qualitatively by choosing parameters corresponding to each region divided by the transition set curves, and the system response can be maintained at the small amplitude near the equilibrium by selecting the appropriate unfolding parameters. We verify the theoretical analysis and calculation of the transition set by showing the consistency of the numerical results obtained by Monte Carlo simulation with the analytical results. The method used in this paper directly guides the design of the fractional order controller to adjust the response of the system

Impact of Industrial Hollowing on Regional Economic Growth Rate: An Empirical Analysis based on Shanghai’s Data

The relation between industrial hollowing-out and Shanghai’s economic growth rate was analyzed by using ordinary least squares and ECM regression model. Data used in the empirical test was a monthly time series data from January 2003 to February 2017. Empirical results show Industrial producer price index, and the total amount of imports has a positive relationship with economic growth rate. However, fixed asset investment, land use cost, and labor resources cost have a negative impact on economic growth rate

Anomalous supercurrent modulated by interfacial magnetizations in Josephson junctions with ferromagnetic bilayers

Based on the Bogoliubov-de Gennes equations, we investigate the transport of the Josephson current in a S/$f_L$-F$_1$-$f_C$-F$_2$-$f_R$/S junction, where S and F$_{1,2}$ are superconductors and ferromagnets, and $f_{L, C, R}$ are the left, central, and right spin-active interfaces. These interfaces have noncollinear magnetizations, and the azimuthal angles of the magnetizations at the $f_{L, C, R}$ interfaces are $\chi_{L, C, R}$. We demonstrate that, if both the ferromagnets have antiparallel magnetizations, the critical current oscillates as a function of the exchange field and the thickness of the ferromagnets for particular $\chi_L$ or $\chi_R$. By contrast, when the magnetization at the $f_C$ interface is perpendicular to that at the $f_L$ and $f_R$ interfaces, the critical current reaches a larger value and is hardly affected by the exchange field and the thickness. Interestingly, if both the ferromagnets are converted to antiparallel half-metals, the critical current maintains a constant value and rarely changes with the ferromagnetic thicknesses and the azimuthal angles. At this time, an anomalous supercurrent can appear in the system, in which case the Josephson current still exists even if the superconducting phase difference $\phi$ is zero. This supercurrent satisfies the current-phase relation $I=I_c\sin(\phi+\phi_0)$ with $I_c$ being the critical current and $\phi_0=2\chi_C-\chi_L-\chi_R$. We deduce that the additional phase $\phi_0$ arises from phase superposition, where the phase is captured by the spin-triplet pairs when they pass through each spin-active interface. In addition, when both the ferromagnets are transformed into parallel half-metals, the $f_C$ interface never contributes any phase to the supercurrent and $\phi_0=\chi_R-\chi_L+\pi$. In such a case, the current-phase relation is similar to that in a S/$f_L$-F-$f_R$/S junction

Critical accumulation of fertilizer-derived uranium in Icelandic grassland Andosol

Long-term phosphorus (P) fertilizer application can lead to an accumulation of uranium (U) in agricultural soil, potentially posing risks on the environment and human health. In this study, we found that such risks could be severe in two long-term grasslands (Andosol) in Iceland (Sámstaðir and Geitasandur) after about 50 years of P fertilization. At Sámstaðir, where P fertilizers were applied at an annual rate of 39.3 kg ha−1 year−1, the soil U concentration increased from 0.65 mg kg−1 in the unfertilized soil to 6.9 mg kg−1 in the fertilized surface soil (0–5 cm). At Geitasandur with P fertilization rate at 78.6 kg ha−1 year−1, the soil U concentration reached 15 mg kg−1. The average annual U accumulation rates were 130 and 310 µg kg−1 year−1, respectively. These values were larger, by up to a factor of ten, than any previously reported rates of fertilizer-derived U accumulation. However, the U concentration in one of the applied P fertilizers was 95 mg U kg−1 fertilizer, similar to the median value of those reported in previous studies, and thus unlikely to be the only factor leading to the high U accumulation rates. By contrast, as our Andosols had low bulk density within a range of 0.2 to 0.5 g cm−3, the annual U inputs to the 0–5 cm soil were 19 g ha−1 year−1 and 32 g ha−1 year−1 at the two sites, respectively, within the range of to-date reported values in agricultural systems. In addition, we found that U was mostly retained in the surface soil rather than mobilizing to deeper soil. This was likely due to the fact that the Andosols were rich in organic matter which promoted U retention. Therefore, the observed high U accumulation rates were a result of the combination of (i) the large amounts of the applied P fertilizers and (ii) the soil properties of the Andosols with low bulk density and elevated organic matter content concentrating U in the upper surface soil. Our study shows that agricultural production systems on Andosols may have already suffered from severe U contamination due to P fertilization. We are therefore calling for future checks and regulations on P fertilizer-related soil U accumulation in these and certain comparable agroecosystems

A Simple Graphene NH₃ Gas Sensor via Laser Direct Writing.

Ammonia gas sensors are very essential in many industries and everyday life. However, their complicated fabrication process, severe environmental fabrication requirements and desorption of residual ammonia molecules result in high cost and hinder their market acceptance. Here, laser direct writing is used to fabricate three parallel porous 3D graphene lines on a polyimide (PI) tape to simply construct an ammonia gas sensor. The middle one works as an ammonia sensing element and the other two on both sides work as heaters to improve the desorption performance of the sensing element to ammonia gas molecules. The graphene lines were characterized by scanning electron microscopy and Raman spectroscopy. The response and recovery time of the sensor without heating are 214 s and 222 s with a sensitivity of 0.087% ppm-1 for sensing 75 ppm ammonia gas, respectively. The experimental results prove that under the optimized heating temperature of about 70 °C the heaters successfully help implement complete desorption of residual NH₃ showing a good sensitivity and cyclic stability

Comercio electrónico conectando China y América Latina a través de la ruta de la seda digital

Latin America is the natural extension of the “Maritime Silk Road” and its exchanges and cooperation with China have become increasingly frequent in recent years. Under the current globale conomic backdrop, e-commerce as an emerging industry is gaining momentum and playing a bigger role in international  cooperation.  The  Belt  and  Road  top-level  design  features  policy  coordination, unimpededtrade, facilities connectivity and people-to-people bond respectively, which play a guiding role in China-LAC cooperation. Coupled with the status quo, the paper will mainly focus on these four sections so as to better analyze the China-LAC cooperation in Silk-Road E-commerce. This paper intends to analyze China-LAC e-commerce cooperation in fields of policy, trade, facilities, and people-to-people contact and study in which areas still remain room for bilateral cooperation and how can both sides better achieve win-win results under the framework of China’s “Belt and Road Initiative”.América Latina es la extensión natural de la “Ruta Marítima de la Seda” y sus intercambios y cooperación con China se han vuelto cada vez más frecuentes en los últimos años. En el contexto económico mundial actual, el comercio electrónico como industria emergente está cobrando impulso y desempeñando un papel más importante en la cooperación internacional. El diseño de alto nivel de la Franja y la Ruta presenta coordinación de políticas, comercio sin trabas, conectividad de instalaciones y vínculo entre personas, respectivamente, que desempeñan un papel rector en la cooperación entre China y ALC. Junto con el statu quo, el artículo se centrará principalmente en estas cuatro secciones para analizar mejor la cooperación entre China y ALC en el comercio electrónico de la Ruta de la Seda. Este documento tiene la intención de analizar la cooperación en comercio electrónico entre China y ALC en los campos de política, comercio, instalaciones y contacto entre personas y estudiar en qué áreas aún quedan espacios para la cooperación bilateral y cómo ambas partes pueden lograr mejores resultados en los que todos ganan en el marco de la “Iniciativa de la Franja y la Ruta” de China