Response Lag Research Articles

Simulation of step input in collective pitch for hovering rotor

Advanced CFD tools are nowadays used routinely for analysis and design of rotorcraft with the research community shifting towards simulations of rotorcraft during maneuvering flight. One of the impediments of this effort is the lack of data for validation, evaluation and thorough assessment of CFD methods when it comes to rotors with time-varying control inputs. This paper presents a first effort to validate CFD tools for step-inputs in rotor control angles against previously un-published experimental data. The experimental study was carried out at the Nanjing University of Aeronautics and Astronautics in China and consists of time varying control inputs for a hovering rotor. The agreement between the simulation and experimental study is good and quantify the overshoot in loads for this dynamic case. The results examine the lag in loads response to and the dynamic response of the wake with recommendations on spatial and temporal resolution to capture these effects.

An integrated model to explain online review helpfulness in hospitality

论：项解释酒店业中在线评论有用性的模型研究目的：本论文提出一项模型, 用于解释在线网络的有用性, 这项模型基于之前文献定义的结构（如评论长短）以及在其他在线评论题材下分析的新结构。而这些结构之前未用来解释有用性。研究设计/方法/途径：样本数据为112,856条TripAdvisor关于21家拉斯维加斯酒店的评论。本论文创建了一种随机森林模型, 用于检测是否一条评论是有用的。研究结果：本论文肯定了提出模型的有效性, 此外, 本论文评估了每个模型结构, 检测其是否解释了有用性。具体地说, 本论文提出了一种新的结构, 经理回复评论的时间长短, 是最相关的结构之一。研究原创性/价值：研究结果表明, 酒店经理应该不仅从酒店角度出发回复最有意思的评论, 而且要快速回复, 以增加其他用户评价这条评论是否对他人决策的有用性。

Homography Estimation of a Moving Planar Scene From Direct Point Correspondence

Homography estimation is an important task in robotics applications, such as landing on moving platforms, docking and refueling, building inspection, and so on. Nonlinear observers depend on an estimate of the group algebra velocity as a feed-forward term to minimize lag in the filter response. When both the camera and the scene are moving, and for perspective image constructs, such as the homography, it is often impossible to directly measure the required group velocity. This article proposes a solution for the case where the motion is periodic, or approximately periodic, with a known period. The approach is based on the internal model principle, where the internal model can be expanded to include a sufficient harmonics of the desired period in order to model complex periodic motions. The novelty of this article lies in formalizing the internal model for observer design to the noncompact Lie group SL(3) and providing a demonstration of the effectiveness of the approach with real-world examples.

Experimental evaluation of indoor thermal environment with modularity radiant heating in low energy buildings

Abstract The air conditioning system in low-energy buildings should be high-efficient because of its limitation on energy consumption and requirement for thermal comfort. This study proposed a novel modularity radiant terminal which can be moved freely in the vertical direction. A series of field experiments on the optimal design scheme of modularity radiant heating terminal was conducted in a laboratory in hot summer and cold winter region of China. Indoor thermal performance with different installation position and area of modularity radiant heating panel were investigated. Results indicated that the modularity radiant heating system can maintain a comfortable indoor environment which the operative temperature can reach 21 °C, the vertical temperature difference below 3 °C and the radiation asymmetry below 4 °C. The design scheme of the modularity radiant heating has significant effects on indoor thermal environment, in which the installation position was a key factor. The modularity radiant panel installed in the middle of the wall and close to the floor can effectively improve the response lag of indoor thermal environment in the operation period and reduce the heat attenuation speed in the shutdown period. The response time of operative temperature at the start period can be reduced for more than 1.5 h and the thermal lag can be increased for more than 2 h at the shutdown period. Besides, the operative temperature can be increased by 1.5 K and the vertical temperature difference and the radiation asymmetry can be reduced by approximately 1 K, respectively. The optimal design of modularity radiant system can simultaneously further improve thermal comfort and realize energy consumption for low energy buildings.

Wind Turbine Speed Compound Control of a New-Type Wind-Electric Hybrid Power Pumping Unit

Because the load of the oil beam pumping unit driven by pure electric motor changes sharply during operation, the power of the driving motor does not match and the energy efficiency is low. In this paper, a new type of wind-driven hydro-motor hybrid power system is proposed. The motor and the hydraulic motor are jointly driven, and the energy is recovered by a hydraulic pump with controllable displacement, so that the speed of the driving motor is relatively stable. In order to control the fan speed and keep up with the drastic changes of the outside wind speed, a control strategy of hybrid power system based on wind speed feed-forward compensation is proposed. Through simulation and experimental results, the following conclusions can be drawn: to begin with, the mathematic model is proved to be effective; next, simulation studies show that the proposed feed-forward control method can improve the response rate as well as reduce the response lag. This research can be a reference for the application of the feed-forward control method on the hybrid power system of beam pumping unit.system.

Research on Compound Coordinated Control for a Power-Split Hybrid Electric Vehicle Based on Compensation of Non-Ideal Communication Network

To improve the mode switching quality of the power-split hybrid electric vehicle (PS-HEV), a compound torque coordinated control strategy is proposed. Aiming at the problem of engine dynamic response lag, the engine real-time torque estimator is designed, and then the torque ripple at the output end of the power coupling mechanism is reduced through the basic motor torque compensation. On this basis, considering the existence of non-ideal communication networks in actual vehicle control systems, the tremendous impact of communication network time delay and interruption on the mode switching stability and vehicle fuel consumption has been deeply revealed. Then the compound coordinated control strategy including the BP-smith predictive controller, motor torque change rate limiting module, network transmission mechanism with fixed communication priority and fault-tolerant torque coordinated control module is put forward and verified by simulation and hardware-in-the-loop test. The results show that the compound coordinated control strategy could still guarantee the system stability, mode switching smoothness and vehicle fuel economy under the interference of stochastic communication delay and interruption.

A country comparison of place-based activity response to COVID-19 policies

The emergence of the novel Coronavirus Disease in late 2019 (COVID-19) and subsequent pandemic led to an immense disruption in the daily lives of almost everyone on the planet. Faced with the consequences of inaction, most national governments responded with policies that restricted the activities conducted by their inhabitants. As schools and businesses shuttered, the mobility of these people decreased. This reduction in mobility, and related activities, was recorded through ubiquitous location-enabled personal mobile devices. Patterns emerged that varied by place-based activity. In this work the differences in these place-based activity patterns are investigated across nations, specifically by focusing on the relationship between government enacted policies and changes in community activity patterns. By addressing five research questions, we show that people's activity response to government action varies widely both across nations as well as regionally within them. Three assessment measures, namely cosine similarity, lag response, and subregional variation, are devised and the results correlate with a number of global indices. We discuss these findings and the relationship between government action and residents' response.

Short communication: The lag response of daily milk yield to heat stress in dairy cows

Previous studies suggest that there exists a lag relationship between daily milk yield and heat stress. The values of heat stress indicators (e.g., temperature-humidity index and ambient temperature) before test day have a simple correlation with daily milk yield on test day. However, the simple correlation might not be the best description because daily milk yield and heat stress indicators have a nature of time series in common, and their correlations are cross correlations that could be affected by autocorrelations. We hope to give a more reliable estimation on the lag relationship of daily milk yield via excluding autocorrelations with transfer function modeling. In this study, we found a lag relationship between daily milk yield and heat stress indicators based on transfer function modeling. Heat stress indicators included ambient temperature and temperature-humidity index. The daily milk yield data from 123 cows were obtained during a consecutive 63-d period (July 10-September 10, 2016). The mean daily milk yield (MY) and the maximum daily ambient temperature (TA_max) satisfied the stationary hypothesis, and the cross correlation between them was calculated. Before excluding autocorrelation, MY at 0 to 4 d after test day had significant cross correlations with TA_max on test day. After excluding the influence of autocorrelations, MY at 1 to 3 d after the test day had significant cross correlations with TA_max on test day. This result suggested that MY would respond to TA_max 1 d after the test day. In addition, the strength of cross correlations between MY and TA_max decreased from 1 to 3 d in sequence, implying a declining lag response of MY that would last for 3 d. The transfer function model for MY and TA_max is written as: MYt = 16.90 + 0.74MYt- 1 - 0.25TA_maxt- 1 + Nt, where Nt is white noise. This model can be used to track and predict the dynamic response of MY to TA_max.

A 7-Year Lag Precipitation Teleconnection in South Australia and Its Possible Mechanism

Precipitation teleconnections with large-scale ocean-atmosphere oscillation systems provide useful information for water management. Here we present a seven-year lag response in South Australia (SA) precipitation to the Southern Annular Mode (SAM) in a positive Interdecadal Pacific Oscillation (IPO) phase. This teleconnection between a positive SAM phase and increased SA precipitation, and vice-versa, statistically consists of three sequential steps : a 27-season lag positive correlation between sea subsurface potential temperature (SSPT) to the south of SA and SAM; a zero-season lag positive correlation between sea surface temperature (SST) and SSPT; and a 2-season positive lag correlation between SA precipitation and SST. Physically, this teleconnection seems to be associated with a supergyre circulation of the Southern Hemisphere Oceans, which transfers SAM signal via subsurface potential sea temperature in the central south Pacific to the south of SA in 27 seasons during the positive IPO phase. Practically, this teleconnection provides a 7-year-lead drought precursor for rain-fed agriculture planning in South Australia. However, the teleconnection disappears in negative IPO phases. The oceanic pathway via the supergyre suggested in this study provides a basis to predict when this seven-year teleconnection may resume in the future based on observation and/or modelling.

The moisture buffering performance of plasters when exposed to simultaneous sinusoidal temperature and RH variations

Wall constructions have the capacity to contribute to the passive regulation of indoor Relative Humidity. This property, referred to as moisture buffering, is linked to the hygroscopicity of materials, which allows materials to store and release moisture from and to the surrounding air, depending on the indoor Relative Humidity levels. Laboratory testing procedures, based on a step-response method, were introduced to quantify moisture buffering. The step response method monitors the change in mass of samples, when subjected to square wave humidity variation and constant temperature. However, those protocol's prescribed testing environmental conditions may not be representative of the materials behaviour in buildings, as the surface of walls is exposed to an indoor environment that changes with respect to the temperature and humidity daily and seasonally. This paper investigates the response of clay and gypsum plasters to quasi sinusoidal and simultaneous humidity and temperature functions. It was experimentally shown that the relative humidity influences the amount of water vapour adsorbed and desorbed by the materials, while temperature impacts the rate and the time lag response of clay and gypsum to the indoor humidity variation. The significance of the investigation is to demonstrate the joint effects of Relative Humidity and temperature on hygroscopic materials and to seek to developing a laboratory test, which can represent the real behaviour of such materials in buildings, which are exposed to sine wave-forms.

Detecting drought-induced GPP spatiotemporal variabilities with sun-induced chlorophyll fluorescence during the 2009/2010 droughts in China

In the parallel with the climate change, droughts have become one of the major climate extremes that induce losses in the terrestrial gross primary production (GPP). However, studying of the drought effects on GPP is still challenging, partly due to the lack of direct observations of GPP at large scales. Aiming to explore the potential of spaceborne sun-induced chlorophyll fluorescence (SIF) in monitoring vegetation droughts and quantifying the drought-induced GPP variabilities, we evaluated GOME-2 SIF with two state-of-art GPP products (i.e. FLUXCOM GPP and GLASS GPP) and flux tower observed GPP, using 2009 summer drought in Northeast China and 2010 spring drought in Southwest China as study cases. We found that SIF was a quantifying indicator of GPP and successfully characterized the temporal dynamics and spatial extents of GPP anomalies during the drought events, as well as accurately estimating the drought-induced GPP losses. Moreover, SIF (R2 = 0.87) performed better than enhanced vegetation index (R2 = 0.78) in capturing the photosynthesis changes induced by droughts, suggesting SIF was more sensitive to plant physiological changes. The strong positive correlations of SIF with Palmer drought severity index (PDSI) and root-zone soil moisture, further gave confidences on the capacity of SIF in vegetation drought monitoring. SIF had a time lag response to both PDSI and soil moisture, which might be attributable to the plants adaptation mechanisms for the drought occurrence and physiological recovery after water stress. Our study demonstrates that satellite-based SIF can achieve real-time vegetation drought monitoring and the assessment of drought-induced GPP anomalies at large scales, thus providing a unique opportunity to study the impacts of drought on vegetation carbon uptake.

Implications of glacial isostatic adjustment on petroleum reservoirs in the Grand banks of Newfoundland

Glacial Isostatic Adjustment (GIA), or postglacial rebound refers to the crustal response to glacial loading and unloading processes. In this investigation, we run numerical simulations using different rheological parameters and ice loading histories to obtain models of the glacial isostatic response for the Grand Banks of Newfoundland. The objective is to assess in general the potential impact of GIA on hydrocarbon reservoirs and trapping structures in terms of tilting, deformation, fault activity or geochemical implications on the trapped fluids. Comparisons may be drawn to related studies, including analogous impacts on reservoirs in the Barents Sea, as well as validation of GIA model predictions of vertical crustal motion using GNSS stations, levelling networks and relative sea level (RSL) observations at numerous sites across eastern Canada. By running a series of GIA models, a range of vertical motion rates are output through time to determine displacement amounts, and calculations are performed on these outputs to disseminate other valuable data attributes such as the displacement gradient and differences in time and space. In general, the vertical motion rate is seen to change drastically over time for certain points, as the lag in response of regions near the ice periphery leads to a distinct pattern of uplift and subsidence. The Grand Banks generally experienced between 57 m of subsidence to 34 m of uplift since the last glacial maximum, depending on the specific location and the GIA model parameters. At the reservoir scale, model results along a 10 km baseline show up to −1.0–1.5 m of differential vertical displacement, which could have led to reservoir tilting or even hydrocarbon migration. As a result of this study, it is clear that there are implications of GIA on hydrocarbon reservoirs since the Last Glacial Maximum, and these effects are ongoing.

Rear-Steering Based Decentralized Control of Four-Wheel Steering Vehicle

In order to improve the lateral and directional performance of vehicles, this paper proposes a novel rear-steering based decentralized control (RDC) algorithm for four-wheel-steering (4WS) vehicles. Based on a linearized single-track vehicle model, a prototype of the RDC algorithm for linear conditions is derived. Linear analysis in frequency domain shows that the RDC can significantly reduce the magnitude and increase the phase lag of sideslip response as well as enlarge the bandwidth of yaw response in a broad frequency range. Through the incorporation of a novel sliding mode controller, the RDC algorithm is further extended for nonlinear applications. Analysis based on nonlinear model shows that, the RDC can guarantee the performance of the closed-loop (CL) system in the presence of uncertainties in system parameters and state feedback values. Moreover, the RDC is robust to arbitrary lateral disturbances and can guarantee that the vehicle converges to reference yaw rate and zero sideslip. Simulation results show that the RDC can effectively improve the lateral and directional performance of the vehicle in comparison with previous control methods. Excellent robustness to external disturbance and road friction variation is reported as well.

Modeling for indoor temperature prediction based on time-delay and Elman neural network in air conditioning system

An effective indoor temperature model would assist in improving energy efficiency and indoor thermal comfort of air conditioning system. However, it is difficult to build an accurate model due to lag response characteristic in the regulation process of indoor temperature. To solve this problem, the modeling and prediction methods for indoor temperature lag response characteristic based on time-delay neural network (TDNN) and Elman network neural (ENN) are presented. Then, taking variable air volume (VAV) air conditioning system as the study object, the effectiveness and practicability of proposed methods are validated using simulation sampling data and real-time operating data. Results indicate that ENN could be considered as a better modeling method for indoor temperature prediction for its simpler network structure, smaller storing space and better prediction accuracy. The contribution of this study is to provide an applicable online ANN modeling method for indoor temperature lag characteristic, and detailed training and validation for online implementation are presented, which will benefit for engineers and technicians to use in practical engineering. Meanwhile, this study provides the reference for online application of advanced intelligent algorithms in the building engineering.

Immune Thrombocytopenia Secondary to COVID-19: a Systematic Review.

Immune thrombocytopenia, often known as immune thrombocytopenic purpura (ITP), has emerged as an important complication of COVID-19. A systematic review was done to analyze the clinical profile and outcomes in a total of 45 cases of new-onset ITP in COVID-19 patients described in literature until date. A comprehensive approach is essential for diagnosing COVID-19-associated ITP after excluding several concomitant factors that can cause thrombocytopenia in COVID-19. Majority of ITP cases (71%) were found to be elderly (> 50 years) and 75% cases had moderate-to-severe COVID-19. Three patients (7%) were in the pediatric age group. Reports of ITP in asymptomatic COVID-19 patients (7%) underscore the need for COVID-19 testing in newly diagnosed patients with ITP irrespective of COVID-19 symptoms amid this pandemic. ITP onset occurred in 20% cases 3 weeks after onset of COVID-19 symptoms, with many reports after clinical recovery. SARS-CoV-2-mediated immune thrombocytopenia can be attributed to the underlying immune dysregulation, susceptibility mutations in SOCS 1, and other mechanisms, including molecular mimicry, cryptic antigen expression, and epitope spreading. No bleeding manifestations were reported in 31% cases at diagnosis. Severe life-threatening bleeding was uncommon. One case of mortality was attributed to intracranial hemorrhage. Secondary Evans syndrome was diagnosed in one case. Good initial response to short course of glucocorticoids and intravenous immunoglobulin has been found with the exception of delayed lag response in one case. Thrombopoietin receptor agonist usage as a second-line agent has been noted in few cases for short duration with no adverse events. In the relatively short follow-up period, four relapses of ITP were found.

Monetary policy impact on the informal economy and response to shocks in the formal economy

In developing countries, there has been a surge in the size of the informal economy in recent years. However, the effect of monetary policy on the informal economy and informal economy responses to shocks from the formal economy is yet to receive empirical attention. Our study aims to explore monetary policy effect on the informal economy and response to shocks in the formal economy in Nigeria for 48 years (1970–2018). Using Autoregressive Distributed Lag and Impulse Response Function, we examined empirically how various monetary policy instruments affect the informal economy and responses to shocks in the formal economy. Our result indicates that credit to the private sector along with the exchange rate had a positive and significant effect on the informal economy both in the long run and short run. The estimate further indicates bank lending rate had a positive and insignificant effect on the informal economy. Our research reveals that in the short run, the informal economy responds positively to shocks in the formal economy while the reserve is the case in the long run. These results underscore the importance of factoring the informal economy in monetary policy decisions.

Integrated control strategy of tractor hydromechanical continuously variable transmission

Given the transmission efficiency fluctuation and response lag problem of hydromechanical continuous variable transmission combined with the complex and variable working environment of a tractor, an integrated control strategy of engine throttle compensation–hydromechanical continuous variable transmission speed regulation is adopted for dual-flow transmission control. On the basis of the estimation of working resistance, a fuzzy algorithm is used to design the throttle compensation law. Considering the maximum driving power of a tractor as the target of variable speed control, an hydromechanical continuous variable transmission efficiency model is established, and the control law of an hydromechanical continuous variable transmission displacement ratio with the maximum driving power of the tractor under any working condition is determined. On the basis of the wavelet neural network proportional–integral–derivative algorithm, the control law of the hydromechanical continuous variable transmission speed regulation is designed, and the parameters of proportional–integral–derivative control are corrected in real time during the control process. Based on MATLAB/Simulink modelling and simulation and the real vehicle verification test, results showed that the influence of hydromechanical continuous variable transmission efficiency fluctuation on the driving power of the entire vehicle, the response lag of the pump-controlled motor system, and the effect of the leakage on the variable speed control and the fluctuation of the working resistance are solved by studying the hydromechanical continuous variable transmission variable speed transmission control strategy. This strategy improves the stability of the tractor speed and ensured the quality of the work, thereby improving the ability of the tractor to adapt to complex working environments.

The influence of COVID-19 on grid parity of China's photovoltaic industry.

With the more efficient involvement of both technology and policy factors in China’s whole industry-chain, the year 2020 is a key period for photovoltaic (PV) industry to achieve grid parity. In this context, COVID-19 may trigger a certain time-delay in new installed PV projects, thereby bringing an uncertain influence on the whole PV industry. To forecast the influence degree and influence cycle of COVID-19 on PV industry, this paper firstly clarifies the key features of epidemic situation as well as the basic rule of such pandemics’ transmission along industry-chain. Then this paper constructs a system dynamics model targeting at cost accounting of PV power generation under the influence of COVID-19 and thus forecasts the variation rules, superposition effects and influence cycle of levelized cost of energy (LCOE) of PV power generation and the operations cost of each sub-system. Empirical results show that PV industry has a lag response to the COVID-19 for 1 quarter and periodic response for 4 quarters, which is mainly embodied in the rise of short-term production cost. At the same time, the influence of COVID-19 on the upstream firms of PV industry is stronger than that on downstream firms. With the gradual recovery of whole industry-chain, LCOE of PV power generation will rapidly return to the previous expected level of grid parity by the end of 2020.

A Pore-Scale Investigation of the Transient Response of Forced Convection in Porous Media to Inlet Ramp Inputs

Abstract This paper investigates the transient response of forced convection of heat in a reticulated porous medium through taking a pore-scale approach. The thermal system is subject to a ramp disturbance superimposed on the entrance flow temperature/velocity. The developed model consisted of ten cylindrical obstacles aligned in a staggered arrangement with set isothermal boundary conditions. A few types of fluids, along with different values of porosity and Reynolds number, are considered. Assuming a laminar flow, the unsteady Navier Stokes and energy equations are solved numerically. The temporally developing flow and temperature fields as well as the surface-averaged Nusselt numbers are used to explore the transient response of the system. Also, a response lag ratio (RLR) is defined to further characterize the transient response of the system. The results reveal that an increase in amplitude increases the RLR. Nonetheless, an increase in ramp duration decreases the RLR, particularly for high-density fluids. Interestingly, it is found that the Reynolds number has almost negligible effects upon RLR. This study clearly reflects the importance of conducting pore-scale analyses for understanding the transient response of heat convection in porous media.

Illuminating the physics of dynamic friction through laboratory earthquakes on thrust faults

Large, destructive earthquakes often propagate along thrust faults including megathrusts. The asymmetric interaction of thrust earthquake ruptures with the free surface leads to sudden variations in fault-normal stress, which affect fault friction. Here, we present full-field experimental measurements of displacements, particle velocities, and stresses that characterize the rupture interaction with the free surface, including the large normal stress reductions. We take advantage of these measurements to investigate the dependence of dynamic friction on transient changes in normal stress, demonstrate that the shear frictional resistance exhibits a significant lag in response to such normal stress variations, and identify a predictive frictional formulation that captures this effect. Properly accounting for this delay is important for simulations of fault slip, ground motion, and associated tsunami excitation.