The Relations of Change Rate of Constitutive Variables for the Freezing and Thawing of Water Saturated Porous Media

The relations of change rate of an independent variable, volumetric strain of the porous skeleton, with the change rates of a kind of constitutive variables, such as porosity, volumetric strain of the solid matrix, are derived from the definition of the porosity of water saturated porous media; and the relations of the change rates of another two independent variables, pressure of the pore liquid water and temperature, with the change rates of another kind of constitutive variables, such as pressure of the pore ice, average pressure of the pore liquid water and ice, and average stress of the solid matrix, are obtained from the Clausius Clapeyron relation in the process of freezing or thawing, definitions of the average pore pressure and effective stress. Based on the hypothesis of linear thermoelasticity, principle of effective stress and these relations, the change rates of all constitutive variables may be described with the change rates of the three independent variables.

Joint Distribution of Wave Periods and Rate of Change of Wave Surface Elevation

The rate of change of wave surface elevation is of much importance in ocean engineering, especially for the determination of the limitation of wave breaking. This paper gives a kind of joint distribution of wave periods and the rate of change of wave surface elevation by means of calculation of the two-order to four-order moment of the frequency spectrum based on the linear wave theory. For the first time, the distribution density function of wave periods determined by peaks is provided, and the conclusion is drawn that the rate of change of wave surface elevation obeys the Rayleigh distribution.

A Review of the Climate-Change-Impacts’Rates of Change in the Arctic

Climate Change is a global phenomenon that has a global scale impact. The current trend of climate change towards the warming of the globe has resulted in various changes in the geological, climatology, social, economical, and bio-logical processes worldwide. Temperature of the globe has increased due to various factors, but anthropogenic plays a major contribution through the heavy input of Greenhouse gases. One of the world’s most remote regions that have been affected by most of the anthropogenic stresses on environmental services is the Arctic Region. The Arctic Region has shown various drastic changes and has shown to be effected by various anthropogenic activities that take place elsewhere. These changes include the ozone hole (resulting from ozone degrading compound emitted heavily by an-thropogenic demands), the accumulation of various persistent and volatile pollutants (i.e. POPs), and the meltdown of the polar ice (among others). These drastic changes are well perceived and well projected for future preparations. However, the question still remains if these impacts would only accelerate change. This paper aims to discuss if these changes are accelerating or happening at a constant rate. In addition, this paper aims to only focus on changes due to global warming and climate changes

Parallel Integrated Model-Driven and Data-Driven Online Transient Stability Assessment Method for Power System

More and more uncertain factors in power systems and more and more complex operation modes of power systems put forward higher requirements for online transient stability assessment methods.The traditional modeldriven methods have clear physical mechanisms and reliable evaluation results but the calculation process is time-consuming,while the data-driven methods have the strong fitting ability and fast calculation speed but the evaluation results lack interpretation.Therefore,it is a future development trend of transient stability assessment methods to combine these two kinds of methods.In this paper,the rate of change of the kinetic energy method is used to calculate the transient stability in the model-driven stage,and the support vector machine and extreme learning machine with different internal principles are respectively used to predict the transient stability in the data-driven stage.In order to quantify the credibility level of the data-driven methods,the credibility index of the output results is proposed.Then the switching function controlling whether the rate of change of the kinetic energy method is activated or not is established based on this index.Thus,a newparallel integratedmodel-driven and datadriven online transient stability assessment method is proposed.The accuracy,efficiency,and adaptability of the proposed method are verified by numerical examples.

Doppler Effect: A Look from Biology Aging

The Doppler effect can be defined as the frequency shift suffered by a wave phenomenon, when there is a difference in relative speed between the waves generated and their source. We know that it occurs in the case of mechanical and electromagnetic waves. We propose to generalize the Doppler effect to the case of frequency changes of certain oscillatory variables in biology before and after puberty, starting from the basis that a metabolically accelerated system is equivalent to a mechanically accelerated system. We then established the following objectives: To verify if there is an average difference in heart and respiratory rates, before and after puberty. To verify the association of these frequency differences with the metabolic activity estimated as basal metabolic rate or BMR. We studied heart and respiratory rate data from healthy people of both sexes, verifying the frequency distribution before and after puberty. We also study the relationship of the frequency distribution with the evolution of the basal metabolic rate throughout life. Analysis of the results shows that the highest heart and respiratory rates occur before puberty, while the lowest rates occur after puberty. A high correlation of the evolution of the variables studied with the evolution of the metabolic acceleration of the system throughout life is also evident. Taking into account that a mechanically accelerated system is equivalent to a metabolically accelerated system, we can conclude that the frequency distribution found is the expression of a generalization of the Doppler effect in the case of biological physical systems.

Trends in gravity changes from 2009 to 2013 derived from ground-based gravimetry and GRACE data in North China

North China is a key region for studying geophysical progress. In this study, ground-based and Gravity Recovery and Climate Experiment（GRACE） gravity data from 2009 to 2013 are used to calculate the gravity change rate（GCR） using the polynomial fitting method. In general, the study area was divided into the Shanxi rift, Jing-Jin-Ji（Beijing-Tianjin-Hebei Province）, and Bohai Bay Basin（BBB） regions. Results of the distribution of the GCR determined from ground-based gravimetry show that the GCR appears to be ＂negativepositive-negative＂ from west to east, which indicates that different geophysical mechanisms are involved in the tectonic activities of these regions. However, GRACE solutions are conducted over a larger spatial scale and are able to show a difference between southern and northern areas and a mass redistribution of land water storage.

Effect of abruptly changing withdrawal rate on solidification microstructure in directionally solidified Al-4.5wt%Cu alloy

Al-4.5wt.%Cu alloy has been directionally solidified at constant and abruptly changing withdrawal rates, respectively. The effects of the withdrawal rate on solidification microstructure, primary dendrite arm spacing(PDAS) and liquid solute distribution in front of the solid-liquid interface were investigated. The experimental results for the PDAS at a constant withdrawal rate agree well with the values calculated by the Hunt, Trivedi and Hunt-Lu models. At an abrupt change in the withdrawal rate, the maximum to minimum ratio of the PDAS at a given solidification parameter, i.e. λ1max/λ1min, is more than 2, and the PDAS values are remarkably history-dependent. Further, the liquid-solute distribution curve based on theoretical calculation shows that the larger the initial withdrawal rate is, the smaller the minimum of liquid solute concentration in front of the solid-liquid interface is after the abrupt change in withdrawal rate.

Variations of the Earth＇s rotation rate and cyclic processes in geodynamics

The authors analyzed the relationship between variations of the Earth＇s rotation rate and the geodynamic processes within the Earth＇s body, including seismic activity, The rotation rate of a planet determines its uniaxial compression along the axis of rotation and the areas of various surface elements of the body. The Earth＇s ellipticity variations, caused naturally by the rotation rate variations, are manifested in vertical components of precise GPS measurements. Comparative analysis of these variations is considered in view of modern theoretical ideas concerning the Earth＇s figure. The results justify further research that is of interest for improvement of space svstems and technologiesi.

An Improved DITC Control Method Based on Turn-on Angle Optimization

Switched reluctance motor(SRM)usually adopts Direct Instantaneous Torque Control(DITC)to suppress torque ripple.However,due to the fixed turn-on angle and the control mode of the two-phase exchange region,the conventional DITC control method has low adaptability in different working conditions,which will lead to large torque ripple.For this problem,an improved DITC control method based on turn-on angle optimization is proposed in this paper.Firstly,the improved BP neural network is used to construct a nonlinear torque model,so that the torque can be accurately fed back in real time.Secondly,the turn-on angle optimization algorithm based on improved GRNN neural network is established,so that the turn-on angle can be adjusted adaptively online.Then,according to the magnitude of inductance change rate,the two-phase exchange region is divided into two regions,and the phase with larger inductance change rate and current is selected to provide torque in the sub-regions.Finally,taking a 3-phase 6/20 SRM as example,simulation and experimental verification are carried out to verify the effectiveness of this method.

A Doppler Location Method Based on Virtual Path Difference

This paper presents a Doppler passive location method for moving targets with fixed single station using the Doppler frequency shift and time difference information.First,based on the relationship between frequency shift and path difference,the virtual path difference is calculated from the measured value of Doppler frequency shift by means of mean value correction.Then,under the assumption that the target is moving at a constant speed along a straight line,two coaxial virtual double base arrays are constructed by using the moving track of the moving target based on the method of fixed period time difference.On this basis,the moving distance of the moving target can be calculated by using the ratio relationship between the frequency difference and the radial distance between the two adjacent detection points in the middle of the array,and the linear solution of the two double base path difference positioning equations.At this point,the relative coordinate position of the moving target can be obtained by directly using the linear solution of the double base path difference positioning equation again.

A novel inertia emulator to reduce the rate of change of frequency for power systems with solar PV and battery energy storage

Energy access,climate change and public health issues are some major drivers for the need for renewable sources.However,most renewable sources,excluding large hydro,have zero or negligible rotational inertia,which is critical to stabilizing the power system after contingency.Therefore,this paper proposes a droop-based inertia emulator to reduce the rate of change of frequency and frequency deviations.The robustness of the controller is analysed by applying various uncertainties and disturbances of power system components that were carried out using DIgSILENT PowerFactory simulations.The obtained results are compared with existing literature and the desired performance shows an improvement in the rate of change of frequency of 34.78%for an IEEE 6-bus system,24.32%for a 12-bus system and 18%for a 39-bus system.

Spatiotemporal variability of permafrost degradation on the Qinghai-Tibet Plateau

Based on data from six meteorological stations in the permafrost regions, 60 boreholes for long-term monitoring of permafrost temperatures, and 710 hand-dug pits and shallow boreholes on the Qinghai-Tibet Plateau （QTP）, the spatiotemporal variability of permafrost degradation was closely examined in relation to the rates of changes in air, surface, and ground temperatures. The de- cadal averages and increases in the mean annual air temperatures （MAATs） from 1961-2010 were the largest and most persistent during the last century. MAATs rose by 1.3 ℃, with an average increase rate of 0.03 ℃/yr. The average of mean annual ground surface temperatures （MAGSTs） increased by 1.3 ℃ at an average rate of 0.03 ℃/yr. The rates of changes in ground temperatures were -0.01 to 0.07 ℃/yr. The rates of changes in the depths of the permafrost table were -1 to ＋10 cm/yr. The areal extent of permafrost on the QTP shrank from about 1.50× 10^6 km^2 in 1975 to about 1.26× 10^6 km^2 in 2006. About 60% of the shrinkage in area of permafrost occurred during the period from 1996 to 2006. Due to increasing air temperature since the late 1980s, warm （〉-1 ℃） permafrost has started to degrade, and the degradation has gradually expanded to the zones of transitory （-1 to -2 ℃） and cold （〈-2 ℃） permafrost. Permafrost on the southern and southeastem plateau degrades more markedly. It is projected that the degradation of permafrost is likely to accelerate, and substantial changes in the distributive features and thermal regimes of permafrost should be anticipated. However, regarding the relationships between degrading permafrost and the degradation of rangelands, it is still too early to draw reliable conclusions due to inadequate scientific criteria and evidence.

Adaptive Wall-Based Attachment Ventilation:A Comparative Study on Its Effectiveness in Airborne Infection Isolation Rooms with Negative Pressure

The transmission of coronavirus disease 2019(COVID-19)has presented challenges for the control of the indoor environment of isolation wards.Scientific air distribution design and operation management are crucial to ensure the environmental safety of medical staff.This paper proposes the application of adaptive wall-based attachment ventilation and evaluates this air supply mode based on contaminants dispersion,removal efficiency,thermal comfort,and operating expense.Adaptive wall-based attachment ventilation provides a direct supply of fresh air to the occupied zone.In comparison with a ceiling air supply or upper sidewall air supply,adaptive wall-based attachment ventilation results in a 15%–47%lower average concentration of contaminants,for a continual release of contaminants at the same air changes per hour(ACH;10 h^(-1)).The contaminant removal efficiency of complete mixing ventilation cannot exceed 1.For adaptive wall-based attachment ventilation,the contaminant removal efficiency is an exponential function of the ACH.Compared with the ceiling air supply mode or upper sidewall air supply mode,adaptive wall-based attachment ventilation achieves a similar thermal comfort level(predicted mean vote(PMV)of0.1–0.4;draught rate of 2.5%–6.7%)and a similar performance in removing contaminants,but has a lower ACH and uses less energy.

A novel index to evaluate discretization methods: A case study of flood susceptibility assessment based on random forest

The selection of a suitable discretization method(DM) to discretize spatially continuous variables(SCVs)is critical in ML-based natural hazard susceptibility assessment. However, few studies start to consider the influence due to the selected DMs and how to efficiently select a suitable DM for each SCV. These issues were well addressed in this study. The information loss rate(ILR), an index based on the information entropy, seems can be used to select optimal DM for each SCV. However, the ILR fails to show the actual influence of discretization because such index only considers the total amount of information of the discretized variables departing from the original SCV. Facing this issue, we propose an index, information change rate(ICR), that focuses on the changed amount of information due to the discretization based on each cell, enabling the identification of the optimal DM. We develop a case study with Random Forest(training/testing ratio of 7 : 3) to assess flood susceptibility in Wanan County, China.The area under the curve-based and susceptibility maps-based approaches were presented to compare the ILR and ICR. The results show the ICR-based optimal DMs are more rational than the ILR-based ones in both cases. Moreover, we observed the ILR values are unnaturally small(<1%), whereas the ICR values are obviously more in line with general recognition(usually 10%–30%). The above results all demonstrate the superiority of the ICR. We consider this study fills up the existing research gaps, improving the MLbased natural hazard susceptibility assessments.

Coastal transgression and regression from 1980 to 2020 and shoreline forecasting for 2030 and 2040,using DSAS along the southern coastal tip of Peninsular India

This study explains the multi-decadal shoreline changes along the coast of Kanyakumari from 1980 to2020.The shorelines are extracted from the Landsat images to estimate the shoreline dynamics and future predictions using Digital Shoreline Analysis System(DSAS).By the estimation of End Point Rate(EPR)and Linear Regression Rate(LRR),it is quantified that the maximum erosion is 5.01 m/yr(EPR)and 6.13 m/yr(LRR)consistently with the maximum accretion of 3.77 m/yr(EPR)and 3.11 m/yr(LRR)along the entire coastal stretch of 77 km.The future shoreline predicted using the Kalman filter forecasted that Inayam,Periyakattuthurai and Kodimunai are highly prone to erosion with a shift of 170 m,157 m and 145 m by 2030 and 194 m,182 m and 165 m by 2040 towards the land.Also,the western coast is highly prone to erosion and it is predicted that certain villages are prone to loss of economy and livelihood.The outcome of this study may guide the coastal researchers to understand the evolution and decisionmakers to evolve with alternative sustainable management plans in the future.

Experimental Study on the Effect of Bed Material Amount and Fuel Particle Size on Load Change of Circulating Fluidized Bed

The large-scale integration of new energy generation has put forward higher requirements for the peak-shaving capability of thermal power.The circulating fluidized bed(CFB)depends on the advantages of a wide load adjustment range and low cost of pollutant control to become a good peak shaving power supply.However,the large delay and inertia caused by its unique combustion mode make it very difficult to change the load quickly.To further understand the factors that affect the load change of CFB,and explore the method of increasing CFB load change rate,the load change experiment on the combustion side was carried out in the 0.1 MW CFB experiment platform.The influence law of bed material amount and fuel particle size on load change of CFB combustion side was revealed for the first time.The results indicated that the increase of bed material amount was beneficial to improve the load change rate on the combustion side of CFB and reduce the carbon content of fly ash,but had no obvious effect on NO_(x)emission.When the bed height at rest increased from 200 mm to 400 mm,the load change rate of the CFB combustion side load from 50%to 75%increased from 0.78%/min to 1.14%/min,and the carbon content of fly ash at 75%load decreased from 26.6%to 24.9%.In addition,the reduction of fuel particle size positively improved the load change rate on the combustion side of the CFB and reduced NO_(x)emission but had a negative effect on reducing the carbon content of fly ash.When the fuel particle size decreased from 0-1 mm to 0-0.12 mm,the load change rate of CFB combustion side load from 50%to 75%increased from 0.78%/min to 1.09%/min,and the NO_(x)emission and carbon content of fly ash at 75%load decreased from 349.5 mg/m^(3)to 194.1 mg/m^(3)and increased from 26.6%to 31.8%,respectively.

变化姿态角下的相位变化率无源定位方法研究(英文)

Technology of passive location has broad prospects in applications. In this paper, the method using the phase rate of change for the single observer passive location is introduced based on existing methods. One can obtain the direction of the target with phase information of two orthogonal interferometers on the observer and the radial distance with the corresponding phase rate of change. Then the target can be located with high speed and precision. A locating approach is given when the flying posture of t...

Strong dependency of lithium diffusion on mechanical constraints in high-capacity Li-ion battery electrodes

The effect of external constraints on Li diffusion in high-capacity Li-ion battery electrodes is investigated using a coupled finite deformation theory. It is found that thinfilm electrodes on rigid substrates experience much slower diffusion rates compared with free-standing films with the same material properties and geometric dimensions. More importantly, the study reveals that mechanical driving forces tend to retard diffusion in highly-constrained thin films when lithiation-induced softening is considered, in contrast to the fact that mechanical driving forces always enhance diffusion when deformation is fully elastic. The results provide further proof that nano-particles are a better design option for nextgeneration alloy-based electrodes compared with thin films.

Fast frequency response of inverter-based resources and its impact on system frequency characteristics

The inertia response and primary frequency regulation capability of synchronous grids are declining owing to the increasing penetration of inverter-based resources. The fast frequency response(FFR) of inverter-based resources is an important mitigation option for maintaining grid security under the conditions of low inertia and insufficient primary frequency response capability. However, the understanding and technical characteristics of the FFR of inverter-based resources are still unclear. Aiming at solving the aforementioned problems, this paper proposes a definition for FFR based on the impact mechanism of FFR on system frequency. The performance requirements of FFR are clarified. Then, the effects of FFR on system frequency characteristics are further analyzed based on steady-state frequency deviation, the initial rate of change of frequency, and the maximum transient frequency deviation. Finally, the system requirements for FFR and its application effects are verified by simulating an actual bulk power grid, providing technical support for subsequent engineering application.