We consider whether survey density forecasts (such as the inflation and output growth histograms of the US Survey of Professional Forecasters) are superior to unconditional density forecasts. The ...unconditional forecasts assume that the average level of uncertainty that has been experienced in the past will continue to prevail in the future, whereas the SPF projections ought to be adapted to the current conditions and the outlook at each forecast origin. The SPF forecasts might be expected to outperform the unconditional densities at the shortest horizons, but it transpires that such is not the case for the aggregate forecasts of either variable, or for the majority of the individual respondents for forecasting inflation.
This article describes calculation of operation modes of railway traction power-supply systems, dc power-supply systems in particular. The procedures recommended for the calculations have been ...obtained under certain assumptions, which simplify the calculations, however, are the reasons of errors. In order to minimize discrepancies between calculations and experimental data, it is required to develop improved simulation models and software complexes on their basis. Brief analysis of potential applications of improved simulation models is given, one of such applications is the determination of parameters and properties of energy-storage systems. An approach is described to development of simulation model on the basis of substitution layout of a network segment, traction specifications of electric rolling stock and other elements. The studies have been performed on the basis of simulation model, which demonstrate that the use of electric energy-storage system is capable to solve certain problems, in particular, to increase carrying capacity and traffic intensity, to increase energy efficiency of electric power traction system. Qualitative estimations of these specifications are given.
•The impact of intra-seasonal climate variability on French crop yields is assessed.•Weather conditions in July and August are the most important for grain maize.•The impact of the meteorological ...drivers is regional dependent for winter wheat.
The impact of intra-seasonal climate variability on inter-annual variation in winter wheat and grain maize yields over 92 French administrative regions is assessed. Observed monthly time series of temperature, precipitation and solar radiation during the growing season are analysed together with reported annual crop yields with a statistical approach based on partial least square regression. Results highlight remarkable spatial differences in the contribution of the main meteorological drivers to crop yield variability and in the timing of the maximum impact. Overall, temperature and global solar radiation are identified as the most important variables influencing grain maize yields over the southern, eastern and northern parts of France, while rainfall variability dominates yields over the central and north-western parts of the country. Positive rainfall anomalies during the summer months lead to an increase in maize yields, while positive temperature and radiation anomalies have the opposite effect. Extensive irrigation suppresses the rainfall signal in dry years. Winter wheat yields are predominantly influenced by temperature variations in eastern France and by rainfall variations over the northern, north-western and south-eastern France. In general, variation in global radiation plays a more important role in the southern than in the northern part of the country. Our study contributes to a better understanding of the impact of intra-seasonal climate variability on crop yields. Potential applications of the inferred models are discussed, especially in terms of seasonal crop yield forecasting and validation of dynamic crop model simulations.
On the Value of Virtual Currencies BOLT, WILKO; VAN OORDT, MAARTEN R.C.
Journal of money, credit and banking,
June 2020, Volume:
52, Issue:
4
Journal Article
Peer reviewed
Open access
Our economic framework suggests that the exchange rate of virtual currency is determined by three components. First, the current value of transactions in virtual currency which absorb part of the ...exchange rate risk. Second, the decisions and expectations of forward‐looking investors to buy virtual currency (thereby effectively regulating its supply). Third, the elements that jointly drive future consumer adoption and merchant acceptance of virtual currency. The model predicts that, as virtual currency becomes more established, the exchange rate will become less sensitive to the impact of shocks to speculators' beliefs. This undermines the notion that excessive exchange rate volatility will prohibit widespread use of virtual currency.
This paper investigates the performance of the credit‐card‐augmented Divisia monetary aggregates in forecasting US inflation and output growth at the 12‐month horizon. We compute recursive and ...rolling out‐of‐sample forecasts using an autoregressive distributed lag model based on Divisia monetary aggregates. We use the three available versions of those monetary aggregate indices, including the original Divisia aggregates, the credit card‐augmented Divisia, and the credit‐card‐augmented Divisia inside money aggregates. The source of each is the Center for Financial Stability. We find that the smallest root mean square forecast errors are attained with the credit‐card‐augmented Divisia indices used as the forecast indicators. We also consider Bayesian vector autoregression for forecasting annual inflation and output growth.
Whistler mode chorus waves appear either as a series of discrete elements (rising or falling tones) or as banded hiss‐like emissions in the dynamic spectrogram. Although the generation of rising‐tone ...chorus waves has been extensively studied, few studies have focused on the generation of hiss‐like emissions. In this paper, using the one‐dimensional (1‐D) general curvilinear particle‐in‐cell (gcPIC) simulation model, we have thoroughly studied the generation mechanisms of hiss‐like emissions. Based on the spectrogram, we first classify hiss‐like emissions into four types (I, II, III, and IV). We find that the type I hiss‐like waves are linearly excited by the anisotropic electrons, while other types are excited through the nonlinear process. For the type I waves, they do not undergo a frequency chirping process and have a relatively broadband spectrum. The high proportion of hot electrons or the large temperature anisotropy of hot electrons will decrease the threshold for nonlinear growth and cause the wave amplitudes to exceed the threshold, leading to the nonlinear generation of type II hiss‐like waves. The fresh hot electrons continually injected into the system with a large drift velocity significantly reduces the time interval between the rising tone elements to form a continuous spectrum, which are the type III waves. The intense and long‐lasting hiss‐like emissions, that is, type IV, which are the most frequently observed, should be generated due to the combined effect of the rapid injection and the high proportion of hot electrons (or the large temperature anisotropy). Our findings provide a comprehensive understanding of the generation of hiss‐like chorus waves in the Earth's magnetosphere.
Plain Language Summary
Chorus waves are important electromagnetic waves in the inner magnetosphere, which typically appears as either hiss‐like emissions or discrete rising or falling tones. Although much effort has been spent on explaining the frequency chirping of chorus waves, the generation of hiss‐like emissions have long been neglected, which are actually the more common spectrogram than the discrete ones. Based on Van Allen Probes data, we first reveal that the hiss‐like emissions can be further divided into four types (I, II, III, and IV). Then, we utilize a one‐dimensional general curvilinear particle‐in‐cell (gcPIC)‐δf model to successfully reproduce the four types of hiss‐like emissions. We propose that the type I hiss‐like waves are linearly excited by the electrons with a temperature anisotropy, while other types undergo the nonlinear growth. The high proportion or large temperature anisotropy of hot electrons will cause the strong nonlinear growth, resulting in the generation of the type II hiss‐like waves. The type III waves depend on the continuous injection of energetic electrons caused by the azimuthal drift. Due to the combined effect of the rapid injection and intense nonlinear growth, the intense and long‐lasting hiss‐like emissions, that is, type IV, which are the most frequently observed, are generated. Our findings provide a deeper insight of the generation of hiss‐like chorus waves in the terrestrial magnetosphere.
Key Points
A 1‐D general curvilinear particle‐in‐cell simulation model is used to study the generation mechanisms of hiss‐like emissions
Based on the spectrogram, the hiss‐like emissions are classified into four types (I, II, III, IV)
The majority of hiss‐like chorus waves in the Earth's magnetosphere are generated through a nonlinear process
Abstract
This study combines simulation and experimental methods to explore the vibration characteristics of a servo controller printed circuit board (PCB). CREO is used to build a simulation model ...based on PCB structure analysis. ANSYS was used to perform finite element simulation analysis of vibration characteristics. The hammering method is used to perform circuit board modal experiments. By comparing the results of simulation and experimentation, the PCB dynamic characteristics are analyzed. It was found that the fixed frequency error of the simulation and the experiment is within 6%, and the first three mode shapes are consistent. Hence, it is suggested to use the simulation model for the subsequent vibration reliability analysis of the electronic product.
Abstract
Inertia and damping in the power system are important parameters in frequency regulation and oscillation suppression. Inertia will reduce the rate and amplitude of frequency changes after ...active power sudden changes. Damping in the system can effectively suppress low-frequency oscillations after grid disturbances. As the penetration rate of wind turbines increases, it will significantly reduce the effective inertia in the power grid and reduce the friendliness of wind power grid connection. To provide better frequency support for the power grid in the event of large disturbances in the power system, this paper proposes a fast frequency control strategy for wind farms that considers the suppression of secondary frequency dips in the power grid. The strategy combines frequency droop control with grid frequency bias control and evaluates the kinetic energy reserve online based on wind power prediction and hourly speed, thus balancing the frequency regulation and suppression of secondary frequency dips in the power grid. A 2.5 MW direct drive wind turbine simulation model was built based on the PSCAD simulation platform, verifying the effectiveness of the proposed comprehensive control strategy.
Abstract
A DC-DC converter voltage balancing controller with added voltage anti overcharging protection device is proposed to address the voltage balancing control problem of supercapacitors used in ...Ships and warships. A simulation model is built in the PSIM environment, and through simulation experiments, this balancing controller can improve the voltage balancing rate, reduce space occupation, and prevent overcharging phenomena. The simulation results show that the improved DC-DC voltage balance controller has a detailed improvement effect on the charging voltage balance of ship supercapacitors.
Abstract
Given the high proportion of wind power frequency/voltage stability problems, the power system based on synchronized coordinates (DFIG) mathematical model of doubly-fed motor, studies a ...current source containing inertial link type wind turbine virtual synchronous control strategy, and the virtual synchronous control loop and the current control design of the inner ring. Established in the Matlab/Simulink simulation model of doubly-fed wind power generator, the virtual synchronous generator realized virtual synchronous generator inertia. Simulation results confirm the validity of the theoretical analysis and the effectiveness of the proposed control strategy.
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