Search

This paper primarily investigates a neural-network-based safe control scheme for solving the optimal control problem of continuous-time (CT) nonlinear systems with asymmetric input constraints under non-zero-sum (NZS) differential game scenarios. Initially, by constructing a novel non-quadratic function, the issue of asymmetric input constraints in the non-zero-sum differential game controllers is addressed. Subsequently, the safe Hamilton-Jacobi-Bellman (HJB) equation is derived from the direct integration of the control barrier function (CBF) into the traditional cost function, ensuring that the system states remain within a safe region. Then, the safe learning control scheme based on single critic neural network (NN) and adaptive dynamic programming (ADP) is proposed to approximate the optimal control strategy, differing from the dual-network update method commonly used in traditional ADP. Based on the constructed neural network weight adjustment rules, the optimal solution to the HJB equation can be derived within the safe learning control framework. Following this, Lyapunov's stability theory demonstrates that the errors in neural network weights and all signals within the closed-loop system are uniformly ultimately bounded (UUB). Finally, the effectiveness of the developed neural-network-based safe learning control method is validated through two simulation results. [ABSTRACT FROM AUTHOR]

This paper investigates a dynamic event-triggered robust safety control method for multiplayer fully cooperative games with mismatched uncertainties and asymmetric input constraints under continuous-time nonlinear systems. Firstly, to address the safety constraints on the system states, a suitable barrier function is proposed to transform the original constrained system into an unconstrained system. Subsequently, through the construction of an auxiliary system, the robust control (RC) problem is transformed into optimal control problem with auxiliary control laws. Secondly, the control laws are subjected to asymmetric constraints by designing a non-quadratic function. Unlike traditional static event-triggered control, a new dynamic event-triggered mechanism is introduced for updating the control laws. In addition, a new critic neural network (NN) weight update method is constructed to approximate the solution of the event-triggered Hamiltonian Jacobi Bellman (HJB) equation by using the concurrent learning technique. Furthermore, Lyapunov's theorem proves that the closed-loop system is uniformly ultimately bounded (UUB). Finally, a simulation example of a single-linked robotic arm is provided to verify the validity of the proposed method in this paper. [ABSTRACT FROM AUTHOR]

The effect of thermal deformation and heat treatment on microstructure and texture of Ti-6Al-4 V alloy was investigated. As for the deformed microstructures, the misorientation angle around 60° gradually intensified with the increase of strain. For the strain rate of 0.001 s−1, the dislocation density value of the base plane is about twice the dislocation density value of the pyramidal. By TEM analyses, the needle-like α with the thickness of 200-700 nm. Only variants α appear in region III and there are four type variants α. The two subvariants share a similar color to the (110) β to share a crystal plane. The maximum polar density of texture can be reduced by decreasing the strain rate. The preferred grain orientation of 45° direction with CD and 45° direction with ND was enhanced in region III, causing by the β → α' and β → α". For heat treatment at 0.1 s−1condition, the spheroidization of lamellar α was boundary splitting. As for ST 1050 °C/1 h/WQ, there are discontinued lamellar α clusters near the GBα and acicular martensite in the β grain. After the SAT 1050 °C/1 h/WQ + 530 °C/6 h/AC processing, the fraction of internal lamellar cluster is reduced, and the fine martensite is gradually surrounded by grain boundary α. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure evolution of as-cast and homogenized Mg-9Gd-4Y-2Zn-0.5Zr alloys during hot compression was studied by electron backscattered diffraction analysis. Specimens were compressed at 420 °C with reductions of 20, 40, and 70%. The results indicated that more recrystallized grains were obtained in the as-cast alloy, which was attributed to many block-shaped phase grains. Under the same conditions, the as-cast alloy had a finer microstructure and weaker texture. In the initial stage, dynamic recrystallization in the form of discontinuous dynamic recrystallization participated in deformation. Further deformation contributed to fine grains in the interior of deformed grains in the form of continuous dynamic recrystallization. Basal slip played an active part in the deformed grains, and the recrystallized grains activated pyramidal slip. [ABSTRACT FROM AUTHOR]

Low biological hydrogen (bioH2) production due to non-optimal metabolic pathways occurs frequently. In this work, magnetic nitrogen-doped activated carbon (MNAC) was prepared and added into the inoculated sludge with glucose as substrate to enhance hydrogen (H2) yield by mesophilic dark fermentation (DF). The highest H2 yield appeared in 400 mg/L AC (252.8 mL/g glucose) and 600 mg/L MNAC group (304.8 mL/g glucose), which were 26.02% and 51.94% higher than that of 0 mg/L MNAC group (200.6 mL/g glucose). The addition of MNAC allowed for efficient enrichment of Firmicutes and Clostridium-sensu-stricto-1, accelerating the metabolic pathway shifted towards butyrate type. The Fe ions released by MNAC facilitated electron transfer and favored the reduction of ferredoxin (Fd), thereby obtaining more bioH2. Finally, the generation of [Fe-Fe] hydrogenase and cellular components of H2-producing microbes (HPM) during homeostasis was discussed to understand on the use of MNAC in DF system. [ABSTRACT FROM AUTHOR]

When the equipment is working, it is very important to avoid the occurrence of malignant accidents by providing a highly reliable safety protection means. In this paper, for multiplayer mixed zero-sum games, an optimal safety tracking control scheme based on adaptive dynamic programming (ADP) is proposed, and a control barrier function (CBF) is introduced into the value function of the system to ensure that the system operates within its safe region. Firstly, through system transformation, the original tracking problem is transformed into a state tracking error problem. Secondly, an augmented Hamilton-Jacobi-Bellman (HJB) equation is derived from the improved augmented error system and the value function. Different from traditional methods, this paper uses a single critic neural network (NN) instead of the actor-critic NN to approximate the Nash equilibrium solution of the system, and introduces a concurrent learning technique that can relax the traditional continuous excitation condition into a simplified condition of recording data. Then, according to the Lyapunov theory, the stability of the system is analyzed in detail. Finally, two simulation examples are used to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

The spark plasma-sintered Ti-6Al-4V alloy was used as experimental specimens to perform the multi-pass hot compression. The deformation temperature was 950, 900, 850 °C, and the compressed amount was 20, 30, 20% corresponding to one pass, two passes and three passes, respectively. The flow behaviors revealed that the curve with the strain rate of 5 s−1 appeared obvious oscillatory phenomenon after peak. Additionally, the curve with strain rate of 0.1 and 1 s−1 almost kept constant after peak stress during the process of two-pass compression. The microstructures showed that the sintered voids with the average diameter of 7.53 μm could be observed in initial Widmanstatten structures with the aspect ratio of 11.49 ± 0.5. The deformed inhomogeneity had prominent influence on the microstructures. For three-pass deformation with the strain rate of 0.1 s−1, the microstructures of severe plastic deformation area were equiaxial microstructures with the grain diameter of 3.82 μm, while the microstructures for medial and small plastic deformation area were dual and Widmanstatten, respectively. With the strain rate of 0.1 s−1, the fraction of dynamic recrystallization (fDRX) increased from 0.034 through 0.112 to 0.440 with the passes increased, and the variation tendency toward average diameter of grain size versus compressed passes shifted reversely. The β→α phase transformation was the main reason for the misorientation angle nearby 60° for one pass with the strain rate of 0.1 s−1. The fDRX declined from 0.440 through 0.225 to 0.297 with raising the strain rate for three-pass deformation, but the grain size changed oppositely. The CDRX and DDRX were both appeared during multi-pass hot deformation. [ABSTRACT FROM AUTHOR]

Widespread air pollutions, such as black carbon over East Asia in recent years, could induce a localized diabatic heating, and thus lead to localized static stability and meridional temperature gradient (MTG) changes. Although effect of static stability and MTG on eddies has been addressed by the linear baroclinic instability theory, impacts of a localized heating on mid-latitude eddy activities have not been well explored and quantified. Via a series of idealized global Held-Suarez simulations with different magnitudes of localized heating at different altitudes and latitudes, responses of mid-latitude eddy activity and circulation to these temperature perturbations are systematically investigated. Climatologically, the localized heating in the lower atmosphere induces a wave-like response of eddy activity near the mid-latitude jet stream. Over the heating region, eddy activity tends to be weakening due to the increased static stability. However, there are cyclonic anomalies over the upstream and downstream of the heating region. The zonal mean eddy activity weakens along the baroclinic zone due to reduced MTG and increased static stability. Furthermore, the response of eddy activity increased as the heating magnitude is increased and moved to higher altitudes. The influence of the heating decreases as the heating is prescribed further away from the climatological mid-latitude jet. This implies that the localized heating is most effective over the region with the maximum baroclinicity. Besides, enhanced storm track downstream of the localized heating area found here suggests that increased aerosols over East Asia might strengthen the North Pacific storm track. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr(VI)) in wastewater is a great risk to the quality of water sources and to human health. Meanwhile, Chinese herb-extraction residues (CHER) are the by-products from the extraction process of Chinese medicine. This study investigated the use of CHER to adsorb Cr(VI) from aqueous solution. Results indicated that adsorption was maximum at solution pH of 2.0 while the Cr(VI) removal efficiencies for chuanxiong rhizome residue (CRR) and Chinese wolfberry residue (CWR) were 86.56 and 99.93%, respectively. Isotherm data were modeled by using Freundlich, Langmuir, and Temkin isotherms. The maximum monolayer adsorption capacities for CWR and CRR were 79.60 and 36.21 mg g, while their corresponding adsorption capacities obtained from experimental data were 37.30 and 32.42 mg g, respectively. However, Freundlich isotherm fitted the data well. Both adsorption and reduction of Cr(VI) to Cr (III) forms followed by complexation onto the adsorbent surfaces favored removing Cr(VI). The results also suggested that the abundant and cheaply available CRR and CWR can be used as efficient adsorbent materials for Cr(VI) removal from wastewater. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the synergistic effects of the process of iron-carbon microelectrolysis (ICME) followed by struvite (MAP) crystallization on treating antibiotic wastewater. Characteristics of ICME effluent depended mainly on the iron to carbon mass ratio (Fe/C). The optimum reaction conditions of Fe/C ratio of 2:1 and reaction time of 90 min were observed. The ICME effluent was further treated by MAP crystallization using NaHPO·12HO and MgCl·6HO as precipitation agents. The results showed that, the Mg/NH -N/PO -P molar ratio of 1:1:1 and pH 8.5, were suitable for the crystallization process, which could obtain high-quality MAP containing 5.18 % N,10.23 % Mg, and 13.83 % P. Optimal total removal rate of COD and NH -N removal rate achieved 84.6 and 89.9 %, respectively. The economic evaluation of NH -N recovery by the synergistic process was also conducted, indicating that the synergistic process had the potential to benefit COD emission reduction and nitrogen recovery. [ABSTRACT FROM AUTHOR]

Northwest China includes Xinjiang Ugyur Autonomous Region, Qinghai Province, Gansu Province, Ningxia Hui Autonomous Region and Shaanxi Province, covering 308×104km2. It is located in the warm-temperate zone and the climate is arid or semi-arid. Precipitation is very scarce but evaporation is extremely high. The climate is dry, the water resources are deficient, the eco-environment is fragile, and the distribution of water resources is uneven. In this region, precipitation is the only input, and evaporation is the only output in the inland rivers, and precipitation, surface water and groundwater change with each other for many times, which benefits the storage and utilization of water resources. The average precipitation in this region is 232 mm, the total precipitation amount is 7003×108 m3/a, the surface water resources are 1891×108 m3/a, the total natural groundwater resources are 1150×108 m3/a, the total available water resources are 438×108 m3/a, and the total water resources are 1996×108 m3/a and per capita water resources are 2278 m3/a. The water resources of the whole area are 5.94×104 m3/(a.km2), being only one-fifth of the mean value in China. Now, the available water resources are 876×108 m3/a, among which groundwater is proximate 130×108 m3/a. [ABSTRACT FROM AUTHOR]

Transpirations of three dominated tree species, namely Mongol Scotch Pine (Pinus sylvestris var. mongolica Litvin), White elm (Ulmus pumila) and Gansu Poplar (Populus gansuensis Wang et Yang) in oasis shelter forest (Linze site) and of two dominated tree species, namely Euphrates Poplar (Populus euphratica Oliv.) and Russia olive (Elaeagnus angustifolia Linn.) in lowland desert (Erjinaqi site) have been estimated using measured sapflow in summer, autumn and winter, 2002 and in spring, 2003. An ENVIS System was used for each site to measure microclimate variables, soil moisture and sapflow every half an hour, and the study time scale is one day. In the 104 days of observation during the growing season at the Linze site, the average daily sapflow of Gansu Poplar is 9.93 L· d-1, and the average transpiration per unit leaf area is 1.99 mm · d-1. For White elm tree, the daily average sapflow is 4.08 L· d-1, while the daily average transpiration per unit leaf area is 0.49 mm · d-1. The values for Mongol Scotch Pine are 3.91 L· d-1 and 0.25 mm · d-1, respectively. In the total 73 days of observation during the growing season at the Erjinaqi site, the daily average sapflows of Russia olive and Euphrates Poplar are 12.1 and 20.97 L· d-1, respectively, and the average transpirations per unit leaf area are 0.22 and 0.31 mm · d-1, respectively. In the observation period of the growing season, tree conductances of Mongol Scotch Pine, White elm, Gansu Poplar or Russia olive show an exponential relationship with the daily average air temperature or vapour pressure deficit, but the relationship is not so obvious between tree conductance and global radiation. The transpiration process of each tree species is affected by all the observed four environmental variables. The response of tree conductance to different climatic factors changes with tree species. The effect of the same factor to the same tree species is also variable in different growing stages. The sapflow of every tree species is relatively large in later spring to early summer, and low in summer, and then reaches its largest value in later September. In the mid-November, the sapflow is relatively large, especially the deciduous tree species. This may be characteristic of the tree species in Arid Regions of Northwest China. [ABSTRACT FROM AUTHOR]

Firstly, the hydrological and meteorological features of the upper reaches of the Yellow River above Tangnag are analyzed based on observation data, and effects of EI Nino and La Nina events on the high and low flow in the upper Yellow River are discussed. The results show El Nino and La Nina events possess consanguineous relationship with runoff in the upper Yellow River. As a whole, the probability of low flow occurrence in the upper Yellow River is relatively great along with the occurrence of El Nino event. Moreover, the flood in the upper Yellow River occurs frequently with the occurrence of La Nina event. Besides, the results also show dissimilarity of El Nino event occurring time exerts greater impact on high flow and low flow in the upper Yellow River, that is, the probability of drought will be greater in the same year if El Nino event occurs in spring, the high-flow may happen in this year if El Nino occurs in summer or autumn; the longer the continuous period of El Nino is, the lower the runoff in the upper Yellow River is. [ABSTRACT FROM AUTHOR]

Magnetic activated carbon (MAC) was fabricated to improve biohydrogen (bio-H2) production. The MAC exhibited higher biocatalytic capability and better microbial immobilization than activated carbon (AC) during the bio-H2 process. Glucose supplemented with 200 mg/L MAC obtained the highest H2 yield of 214 mL/g glucose, much higher than that (130 mL/g glucose) of the control group without MAC. Suitable dosage such as 300 mg/L AC or 200 mg/L MAC promoted volatile fatty acid (VFA) formation and H2 generation. Besides, the metabolites showed that AC or MAC did not change the bio-H2 evolution pathway. Some possible biochemical mechanisms were as follows: MAC served as a microbial carrier to promote cell colonization and electron transfer rate, and it released Fe3+ to enhance glucose acidogenesis and Fe2+ to increase microbial concentration and activity in the bio-H2 evolution. [ABSTRACT FROM AUTHOR]

This work has been performed to investigate the use of lime mud filtrate (LMF) pretreatment to enhance hydrogen (H2) evolution from sewage sludge (SS). The SS samples were pretreated with LMF (pH 8.0-11.0) at 55 °C for 48 h, prior to the H2 fermentation. The maximum H2 yield of 38.30 ml/g-VS (volatile solid) was obtained from the SS pretreated by LMF pH of 10.0, with the corresponding lag time of 3.10 h, which was well described by the modified Gompertz model. Adequate pH of LMF facilitated the solubilization of SS and the release of organic matters, providing adequate substrates for subsequent bio-H2 evolution. The soluble chemical oxygen demand was increased from 25.0 to 91.7%, as compared with the control test without LMF soak. However, further increase in pH of LMF could decrease the concentration of available substrate, thus reducing the H2 yield. This technique revealed sustainable waste management and energy recovery. [ABSTRACT FROM AUTHOR]