Zhang Model Research Articles

Spatio-temporal assessment of annual water balance models for upper Ganga Basin

Abstract. The upper Ganga Basin in Uttarakhand, India, has high hydropower potential and plays an important role in the development of the state economy. Thus, an accurate knowledge of annual water yield is of paramount importance to this region. This paper deals with use of contemporary water yield estimation models such as the distributed Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model and the Lumped Zhang model and their validation to identify the most suited one for water yield estimation in the upper Ganga Basin. In previous studies utilizing these models, water yield was estimated by considering a single value of some important model parameters for the entire basin, which in fact show distributed variation at a finer (pixel) scale. Therefore, in this study, pixel-level computations are performed to assess and ascertain the need for incorporating the spatial variation of such parameters in model applications. To validate the findings, the observed sub-basin discharge data are analyzed with the computed water yield for 4 decades, i.e., 1980, 1990, 2001 and 2015. The results obtained are in good agreement with the water yield obtained at the pixel scale.

An existence result for a constrained two-phase transition model with metastable phase for vehicular traffic

In this paper we study a phase transition model for vehicular traffic flows. Two phases are taken into account, according to whether the traffic is light or heavy. We assume that the two phases have a non-empty intersection, the so called metastable phase. The model is given by the Lighthill–Whitham–Richards model in the free-flow phase and by the Aw–Rascle–Zhang model in the congested phase. In particular, we study the existence of solutions to Cauchy problems satisfying a local point constraint on the density flux. We prove that if the constraint F is higher than the minimal flux \(f_\mathrm{c}^-\) of the metastable phase, then constrained Cauchy problems with initial data of bounded total variation admit globally defined solutions. We also provide sufficient conditions on the initial data that guarantee the global existence of solutions also in the case \(F < f_\mathrm{c}^-\). These results are obtained by applying the wave-front tracking technique.

A Semianalytical Productivity Model for a Vertically Fractured Well With Arbitrary Fracture Length Under Complex Boundary Conditions

Summary Vertically fractured wells are used widely to achieve efficient development of low-permeability reservoirs and unconventional tight reservoirs. Currently, there are some commonly adopted productivity models for a fractured vertical well, including the Giger (1985) model, the Economides model (Economides et al. 1989), the Joshi (1991) model, the Guo model (Guo and Evans 1993), the Zhang (1999) model, and others. However, these models are only suitable for either short fractures or long fractures, and thus cannot satisfy the need for arbitrary-length fracture selection. In addition, these models have certain requirements for boundary conditions, and few models consider the nonuniform flow in actual hydraulic factures. Therefore, it is desirable to establish a productivity model for vertically fractured wells with arbitrary fracture length under complex boundary conditions. In this paper, first, we evaluate the existing fractured-vertical-well productivity models in detail. After that, on the basis of the potential superposition principle and mirror-image method, we develop the productivity model for a fractured vertical well with arbitrary fracture length under different boundary conditions. Grounded in this model, further considering the frictional pressure drop caused by fracture-flow nonuniformity, we establish the productivity equation of a finite-conductivity-fracture vertical well with nonuniform flow in the fracture. Finally, after comparing with the existing model under certain conditions, the reliability of the proposed model is verified successfully. Results show that the Giger model assumes that the boundary in the fracture-extension direction is impermeable, and the pressure wave reaches the boundary earlier than the constant-pressure boundary, which is perpendicular to the extension direction of the fracture, whereas both the Economides model and the Joshi model assume that the boundary in the fracture-extension direction is far, and is always farther than the boundary perpendicular to the direction of the fracture extension. The results forecast by the previous models will deviate greatly from actual well-production performance, if the real field case cannot meet the requirements of these models. The proposed model is not only in good agreement with the previous models at given conditions, but is also suitable for fractured vertical wells under arbitrary-length fractures and complex boundary conditions. Compared with the existing models, the correctness and reasonableness of the model are shown, and the application of the proposed model is broadened. For the development of low-permeability and unconventional tight oil and gas reservoirs with fractured vertical wells or fractured horizontal wells, the establishment and application of this model have great theoretical significance and application value for production prediction. This model can be a foundation or reference for productivity prediction of low-permeability and unconventional tight oil and gas reservoirs with fractured vertical wells or fractured horizontal wells.

Coexistence of scale-invariant and rhythmic behavior in self-organized criticality.

Scale-free behavior as well as oscillations are frequently observed in the activity of many natural systems. One important example is the cortical tissues of mammalian brain where both phenomena are simultaneously observed. Rhythmic oscillations as well as critical (scale-free) dynamics are thought to be important, but theoretically incompatible, features of a healthy brain. Motivated by the above, we study the possibility of the coexistence of scale-free avalanches along with rhythmic behavior within the framework of self-organized criticality. In particular, we add an oscillatory perturbation to local threshold condition of the continuous Zhang model and characterize the subsequent activity of the system. We observe regular oscillations embedded in well-defined avalanches which exhibit scale-free size and duration in line with observed neuronal avalanches. The average amplitude of such oscillations are shown to decrease with increasing frequency consistent with real brain oscillations. Furthermore, it is shown that optimal amplification of oscillations occur at the critical point, further providing evidence for functional advantages of criticality.

Existence of BV solutions for a non-conservative constrained Aw–Rascle–Zhang model for vehicular traffic

The main aim of this paper is to study the Aw–Rascle–Zhang (ARZ) model with non-conservative local point constraint on the density flux introduced in [10], its motivation being, for instance, the modeling of traffic across a toll gate. We prove the existence of weak solutions under assumptions that result to be more general than those required in [11]. More precisely, we do not require that the waves of the first characteristic family have strictly negative speeds of propagation. The result is achieved by showing the convergence of a sequence of approximate solutions constructed via the wave-front tracking algorithm. The case of solutions attaining values at the vacuum is considered. We also present an explicit numerical example to describe some qualitative features of the solutions.

Comparative Analysis of All-Sky Luminous Efficacy Models Based on Calculated and Measured Solar Radiation Data of Four Worldwide Cities

Luminous efficacy model uses solar radiation data to generate illuminance data, and its performance also depends on the quality of solar radiation data. Various luminous efficacy models are reviewed and evaluated to select a universal luminous efficacy model. Since most luminous efficacy models are fitted with specific local climate characteristics, the model that has the least locality as well as accuracy is a mandatory requirement. Three representative luminous efficacy models are selected and evaluated with measured solar radiation and illuminance data from four worldwide cities. It was found that all the evaluated models provide good predictions (over 0.96 R2 value) for both global and diffuse illuminance. Among them, the Perez luminous efficacy model shows the highest performance in terms of accuracy and bias. However, illuminance data prediction based on estimated solar radiation data is more common practice rather than those from measured solar data. The performance of the selected luminous efficacy models is evaluated when recently proposed universal solar radiation model supplies predicted solar radiation data. The result indicates that the quality of estimated solar radiation data has a much deeper impact on the performance of the luminous efficacy model. Within the current limited technology and measured data resource, the consecutive processing of the modified Zhang and Huang solar model and Perez luminous efficacy model could provide the best option to predict both global and diffuse solar radiation and illuminance. But, users of the model-based illuminance data should interpret their simulation results with the error (30%~40% in RMSE and ±6% in MBE) in predicting global and diffuse illuminance.

S-N Curve Models for Composite Materials Characterisation: An Evaluative Review

S-N behavior has been a backbone of material fatigue life studies since the 19th century. Numerous S-N curve models have been produced but they have been arbitrarily chosen in numerous research works dominantly for composite materials. In this paper, they were critically reviewed and evaluated for capability using the following criteria: data fitting capability, efficiency of curve fitting, applicability to data sets at various stress ratios (−0.43, −1, −3, 0.1, and 10), representability of fatigue damage at failure, and satisfaction of the initial boundary condition. The S-N curve models were found to be in two categories—one for fatigue data characterization independent of stress ratio, and the other for those designed for predicting the effect of stress ratio. The models proposed by Weibull, Sendeckyj, and Kim and Zhang for fatigue data characterization appeared to have the best capabilities for experimental data obtained from Weibull for R = −1, from Sendeckyj for R = 0.1, and from Kawai and Itoh (for R = −0.43, −3, and 10). The Kim and Zhang model was found to have an advantage over the Weibull and the Sendeckyj models for representing the fatigue damage at failure. The Kohout and Vechet model was also found to have a good fitting capability but with an inherent limitation for shaping the S-N curve at some stress ratios (e.g., R = −0.43). The S-N curve models developed for predicting the effect of stress ratio were found to be relatively inferior in data fitting capability to those developed directly for fatigue data characterization.

Constitutive Modeling of the High-Temperature Flow Behavior of α-Ti Alloy Tube

In the hot metal gas forming process, the deformation conditions, such as temperature, strain rate and deformation degree, are often prominently changed. The understanding of the flow behavior of α-Ti seamless tubes over a relatively wide range of temperatures and strain rates is important. In this study, the stress–strain curves in the temperature range of 973-1123 K and the initial strain rate range of 0.0004-0.4 s−1 were measured by isothermal tensile tests to conduct a constitutive analysis and a deformation behavior analysis. The results show that the flow stress decreases with the decrease in the strain rate and the increase of the deformation temperature. The Fields–Backofen model and Fields–Backofen–Zhang model were used to describe the stress–strain curves. The Fields–Backofen–Zhang model shows better predictability on the flow stress than the Fields–Backofen model, but there exists a large deviation in the deformation condition of 0.4 s−1. A modified Fields–Backofen–Zhang model is proposed, in which a strain rate term is introduced. This modified Fields–Backofen–Zhang model gives a more accurate description of the flow stress variation under hot forming conditions with a higher strain rate up to 0.4 s−1. Accordingly, it is reasonable to adopt the modified Fields–Backofen–Zhang model for the hot forming process which is likely to reach a higher strain rate, such as 0.4 s−1.

Shadowing Correlation: Empirical Results for mm-Wave Wireless Links in Urban Street Canyons

To the best of our knowledge, this letter reports the first measurement campaign aimed at modeling the empirical large-scale/shadowing decorrelation distance in urban street canyons at 60 GHz. The observed path-loss exponents were close to Friis. Our results also show that the decorrelation distance is smaller than 40 wavelengths for the three tested scenarios. We also report that Zhang's model for the autocorrelation function of shadow fades provides a better fit than the Gudmundson's model.

Oil price forecasting using a hybrid model

Forecasting oil prices is an important and challenging matter, because of its impact on many economic and non-economic factors. Because factors such as economic growth, political events, and psychological expectations affect oil prices, forecasting oil prices has great uncertainty. There is no consensus among researchers about the techniques and models used to predict oil prices; hence, methods of forecasting with higher accuracy and lower error should be developed. It is important to combine different models and investigate different approaches, especially time-varying forms. In this paper, the exponential smoothing model (ESM), autoregressive integrated moving average model (ARIMA), and nonlinear autoregressive (NAR) neural network are combined in a state-space model framework to increase the accuracy of forecasting that accounts for problems in accurate diagnosis of linear and nonlinear patterns in economic and financial time series such as for crude oil prices. In the proposed hybrid model (PHM), time-varying weights for each model are determined by Kalman filter. The PHM is used on monthly OPEC crude oil prices and WTI crude oil spot prices. The numerical results show a decrease in forecasting error using the PHM compared to its constructive models, the equal weights hybrid model (EWH), the genetic algorithm weights hybrid model (GWH), and the Zhang's hybrid model (ZHM).

Ionic Mechanism of Propagation in Human Purkinje fiber Cells: Role of Calcium Ions and Calcium Channels - a Simulation Study

An important ailment that requires treatment by the physician is cardiac failure (“Heart Failure (HF)”), which usually decreases the contractility of the myocardium. The Purkinje Fibre Cells (PFC) augurs to be an important biological network of the human cardiac ventricular conduction system. It assuages to be tertiary pacemaker of the heart which synchronizes the ventricular conduction. This work analyzes the effects of calcium ionic mechanism of propagation using the Zhang model. The strength of contraction of cardiac muscle depends to a great extent on the concentration of calcium ions in the extracellular fluids. The calcium ions also play vital role in excitation, contraction coupling and cardiac muscle relaxation. The model attempts to increase the influx of calcium concentration (0.000156 mM) from the normal Ca2+ (0.000102 mM) value and also to increase the extracellular calcium concentration ([Ca2+]o) (3 mM). The result show that the internal rise of calcium concentration increased excitability of PFC and maintain plateau potential throughout propagation. Similarly, the high calcium level in extracellular and low calcium level in intracellular decreased excitability of PFC and affect propagation diastole relaxation period. The Calcium channels appear to play a major role in sustaining conduction and propagation when low calcium level in intracellular fluids. The abnormal calcium concentration may affect the PFC excitability and Conduction velocity, which in turn can lead to cardiac ventricular arrhythmias.

The impact of hourly solar radiation model on building energy analysis in different climatic regions of Turkey

The purpose of this study is to investigate the effect of solar radiation models on the determination of energy performance of a single-family house assisted with renewable energy system including photovoltaic panels and solar water heater. An Angstrom-Prescott type solar radiation model was compared with Zhang and Huang model derived based on hourly meteorological data of 12 locations in Turkey. Since regression coefficients of the Zhang and Huang model are valid for China, new regression coefficients were derived by using local meteorological data. A clear distinction could not be observed in simulated annual heating load intensity for each model since the average relative deviation of the models’ results was 2.5%. However, the average deviation was 12.5% for space cooling load intensity. Primary energy ratings (PER) and the renewable energy ratio (RER) were determined for each location. For total PER, the highest deviation was 4.6% and 3.3% for Mersin and Mugla, respectively. For the other locations, this parameter deviates between 0.02%–2.11%. The highest RER was 18.6% for Mersin.

Effect of carbon nanofiber concentration on mechanical properties of porous magnesium composites: Experimental and theoretical analysis

This study investigated the effect of the reinforcing phase – carbon nanofiber (CNF) concentration on mechanical properties of fabricated porous magnesium-matrix composites with 34% porosity. The average yield strength and the average ultimate compressive strength increased steeply when the CNF concentration increased from 0.05% to 0.2%, and increased gradually when the CNF concentration increased from 0.2% to 1.5% and from 2% to 5%. The mechanical properties of porous magnesium-matrix composite with 1.5% CNF are the highest among the studied composites, and the average yield strength, the average ultimate compressive strength, and the energy absorption capability were enhanced by 54%, 49%, and 43% respectively from those for porous magnesium without CNF. The Rule of mixture model, Strengthening factor model, and Zhang & Chen model provided the yield strength predictions that match well with the experimental data for the composites with less than 2% CNF, and the strengthening mechanism includes Orowan strengthening and thermal expansion coefficient mismatch strengthening. The Shear Lag model and Rule of mixture model provided the yield strength predictions that match well with the experimental data for the composites with more than 2% CNF, and load transfer from magnesium to CNF is the dominating strengthening factor.

The Cauchy problem for the Aw–Rascle–Zhang traffic model with locally constrained flow

We study the Cauchy problem for the Aw–Rascle–Zhang model for traffic flow with a flux constraint located at [Formula: see text]. The purpose of such a traffic model is to describe an obstruction in a road, such as a toll gate or a construction site. We consider here the concept of solutions introduced by Garavello and Goatin in 2011, which conserves the total number of cars flowing through the obstruction, but does not conserve the generalized momentum. We prove the existence of such solutions to the Cauchy problem by using the wavefront tracking method. We also compare our results with another concept of solutions introduced also by Garavello and Goatin in 2011 for the same model with a flux constraint. For this second formulation, Andreianov, Donadello, and Rosini had also proved the existence of solutions to the Cauchy problem.

A-26 水回り空間を中心とした省エネルギー性と快適性に関する研究 : (第14報)65MNモデルとZhangモデルを用いた生理量・心理量の予測

A-26 水回り空間を中心とした省エネルギー性と快適性に関する研究 : (第14報)65MNモデルとZhangモデルを用いた生理量・心理量の予測

Temperature- and texture-dependent dielectric model for frozen and thawed mineral soils at a frequency of 1.4 GHz

A single-frequency dielectric model at 1.4GHz for frozen mineral soils was developed, with the temperature and gravimetric clay content varying from −1 to −30°C and from 9.1 to 41.3%, respectively. The model is based on the refractive mixing dielectric model and the dielectric data measured for the three typical soils collected in the Yamal tundra. The refractive mixing dielectric model was applied to fit the measured dielectric data as a function of soil moisture at a number of fixed temperatures. As a result, the parameters of the developed model were derived as a function of temperature and texture. This set of parameters consists of the maximum gravimetric fraction of unfrozen bound water and the values of the complex refractive indexes relating to soil solids, unfrozen bound water, and moistened ice. The developed model for frozen mineral soils in conjunction with the previously developed by us dielectric model for thawed mineral soils is considered as an integral dielectric model which is applicable for permittivity calculations of soil in both thawed and frozen states.The developed integral dielectric model for frozen and thawed mineral soils was validated using the dielectric data for five measured soils, and the statistical errors were estimated in terms of the root mean square error and the determination coefficient. In addition, the only known in the literature dielectric model for frozen soils suggested by Zhang was validated based on dielectric data for soils measured in this research. The comparative analysis proved substantially better accuracy of predictions in the case of the developed model as compared to those related to the Zhang model.

Response to Comment on "Permanent human occupation of the central Tibetan Plateau in the early Holocene".

We show that Zhang and Li's sedimentological model for the Chusang travertine neglects the three-dimensional information from multiple outcrops and that their optically stimulated luminescence (OSL) age of about 20,000 years for the human imprints is untenable. We highlight the robustness of our chronology and explore reasons why Zhang and Li's OSL age is a gross overestimation of the real depositional age of the imprinted travertine.

Evaluation of shear stress and unit stream power to determine the sediment transport capacity of loess materials on different slopes

This study aims to evaluate the relationship between loess soil-based sediment transport capacity and the most well-known and extensively used shear stress and unit stream power for different steep slopes. This study also determined the suitability of shear stress- and unit stream power-based transport capacity functions for rill flow on non-erodible bed. Loess soil was collected from Ansai County, which is located in a typical loessial region in China’s Loess Plateau. The median diameter of the loess soil was 0.04 mm. The experiment was conducted in a rill flume with a soil-feeding hopper. The slope gradients in this study ranged from 10.51 to 38.39%, and the flow discharges per unit width varied from 1.11 × 10−3 to 3.78 × 10−3 m2 s−1. The sediment transport capacity was measured for each combination. Results showed that Tc can be effectively described by the power function shear stress-based equations for various slope gradients with R 2 > 0.94 and P < 0.01. Shear stress was a good predictor of Tc for different slope gradients with the Nash–Sutcliffe model efficiency (NSE) from 0.94 to 0.99. Moreover, shear stress was better in predicting Tc when the slope gradient was above 21.26%. Tc can be efficiently described by the power function unit stream power-based equations for various slope gradients with R 2 > 0.95 and P < 0.01. Unit stream power was a good predictor of Tc for different slope gradients with NSE that ranged from 0.95 to 0.99. The unit stream power predicted Tc better when the slope gradient was above 26.79%. Unit stream power was more satisfied than shear stress for predicting Tc under different slope gradients. The unit stream power-based LISEM, which was multiplied by 0.62 (i.e., the correction coefficient), predicted well the sediment transport capacity of the rill flow in our experiment, where NSE = 0.93. The shear stress-based Zhang model, which was multiplied by the correction coefficient of 0.77, adequately predicted the sediment transport capacity of rill flow in our experiment, where NSE = 0.81. By performing the controlled rill flume experiments, this study showed that shear stress and unit stream power strongly influenced Tc for certain slope gradients under non-erodible conditions.

Comparing traffic state estimators for mixed human and automated traffic flows

This article addresses the problem of modeling and estimating traffic streams with mixed human operated and automated vehicles. A connection between the generalized Aw Rascle Zhang model and two class traffic flow motivates the choice to model mixed traffic streams with a second order traffic flow model. The traffic state is estimated via a fully nonlinear particle filtering approach, and results are compared to estimates obtained from a particle filter applied to a scalar conservation law. Numerical studies are conducted using the Aimsun micro simulation software to generate the true state to be estimated. The experiments indicate that when the penetration rate of automated vehicles in the traffic stream is variable, the second order model based estimator offers improved accuracy compared to a scalar modeling abstraction. When the variability of the penetration rate decreases, the first order model based filters offer similar performance.

고로슬래그 미분말 혼입 시멘트 페이스트의 프랙탈 특성에 관한 기초적 분석

This study aimed to conduct the basic analysis on the fractal characteristics of cementitious materials. The pore structure of cement paste incorporating ground granulated blast furnace slag (GGBFS) was measured using mercury intrusion porosimetry (MIP) and the fractal characteristics were investigated using different models. Because the pore structure of GGBFS-blended cement paste is an irregular system in the various range from nanometer to millimeter, the characteristics of pore region in the different scale may not be adequately described when the fractal dimension was calculated over the whole scale range. While Zhang and Li model enabled analyzing the fraction dimension of pore structure over the three divided scale ranges of micro, small capillary and macro regions, Ji el al. model refined analysis on the fractal characteristics of micro pore region consisting of micro I region corresponding to gel pores and micro II region corresponding to small capillary pores. As the pore size decreased, both models suggested that the pore surface of micro region became more irregular than macro region and the complexity of pores increased.