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Reinforcement learning is one of the most important methodologies in artificial intelligence and has achieved unprecedented success for addressing the fundamental decision-making tasks in various fields, including financial decisions, navigation, and robotic control tasks. However, the current reinforcement learning faces two well-recognized challenging problems, namely, trapping in the local optima and weak generalization, limiting its ability and performance to tackle complex and dynamic decision making tasks. Here, inspired by human intelligence, we present a new framework, called the \emph{cognitive escape reinforcement learning} (CERL), that has the cognition escape module and the semantic cognition module, for avoiding local optima and achieving strong generalization. Moreover, we elaborate on CERL in a classical and complex decision-making task, namely, visual navigation. Extensive experiments demonstrate the efficacy of our proposed CERL framework. Its navigation performance is also remarkably superior to those of the state-of-the-art methods. Furthermore, it can achieve the highest navigation success rate, which is more than 6\% higher than that of the best agent among the existing ones. The required path length is shortened by more than 29\% and delivers real-time performance. Our presented reinforcement learning-based framework opens up a new direction for tackling future complex decision-making tasks rapidly and with high performance.

Glycerol dialkyl glycerol tetraethers (GDGTs) are widespread but unique membrane23 spanning lipids of many Archaea and some Bacteria. However, their specific biological sources and the associated environmental controls on their distribution remain unclear, especially in lacustrine settings, hindering our understanding of these compounds and their application as environmental proxies. Here we investigated the GDGT distributions across a large bottom water dissolved oxygen (DO) gradient (0.10-7.20 28 mg/L) using surface sediments of Lake Yangzonghai, a warm monomictic lake in southwestern China. We show that the distributions of both branched (br) and isoprenoidal (iso) GDGTs co-vary significantly with bottom water DO concentration. The relative abundances of tetramethylated brGDGTs, 5-methyl penta- and hexamethylated brGDGTs and isoGDGT-0 show a stepwise increase as bottom water DO concentration decreases. On the other hand, the relative abundances of 6-methyl penta- and hexamethylated brGDGTs and crenarchaeol exhibit a stepwise decline with a decrease in bottom water DO concentration. Genetic data indicate these DO-induced changes in GDGT parameters are related to changes in the bacterial and archaeal communities across the oxycline in the lake. For example, the high abundance of isoGDGT-0 in low DO samples coincides with a high abundance of methanogenic archaea and Bathyarchaeota. We propose that brGDGT-producing bacteria might include a diversity of other phyla in addition to the proposed source organism acidobacteria; different groups of anaerobic and aerobic bacteria are likely to contribute to the increased abundance of 5-methyl brGDGTs and 6-methyl brGDGTs in low and high DO zones, respectively. Consequently, the MBT’ and MBT’6ME brGDGT indices display strong correlations with DO concentration. Importantly, the MBT’5ME index is not significantly influenced by changes in DO concentration, suggesting that this index might be more resilient to these impacts and more suitable to reconstruct temperature in lake systems.

Bacterial branched and archaeal isoprenoid glycerol dialkyl glycerol tetraethers (brGDGTs and isoGDGTs, respectively) have become important tools for the paleoclimate reconstruction of lacustrine systems. However, it is still unclear how geochemical proxies based on GDGTs, particularly in lake surface sediments, respond to seasonal environmental changes in shallow water lakes, whose sediment cores are increasingly being used for paleoenvironmental reconstruction. In this study, we collected samples from the top 0–2 cm of sediments and water column suspended particulate matter (SPM) at a monthly interval from June 2015 to May 2016 in Lake Donghu, a shallow lake in central China. An updated liquid chromatography method was used to separate the 5- and 6-methyl brGDGTs. A remarkable difference between the lake sediments, SPM, and catchment soils suggested that microorganisms inhabiting the surface sediments contributed a significant proportion of isoGDGTs and brGDGTs to the GDGT pool in the lake sediments. We found a clear seasonality in the concentration and distribution of core lipid (CL) isoGDGTs and brGDGTs in the lake surface sediments, in contrast to the absence of seasonality in brGDGTs in mid-latitude soils reported by previous studies. The intact polar lipid/CL ratios for both isoGDGTs and brGDGTs in the lake surface sediments were significantly higher than those in SPM and catchment soils and were higher in the warm seasons than in winter. This collectively suggested that the turnover of brGDGTs in the lake sediments was faster than that in soils. Furthermore, the GDGT-0/Cren ratio for the lake sediments exhibited a negative correlation with dissolved oxygen in the water column. The cyclisation degree of C5-methylated brGDGTs (CBT5ME) was strongly related to water pH. Seasonal temperature variation clearly impacted the methylation degree of C6-methylated brGDGTs (MBT′6ME) but had no influence on C5-methylated brGDGTs (MBT′5ME), as opposed to the dependence of MBT′5ME on temperature in global soils, peatlands and African lakes. Due to the fast turnover rate and the sensitive response to seasonality, we suggest that the seasonal variation of fossil GDGTs in lake sediments should be considered when developing a calibration using fossil GDGTs in shallow-water lake surface sediments.

A self-assembled functionalized metal-organic framework, Zn4O(NH2BDC)3 microcrystalline (IRMOF3) could be prepared by washing complex with DMF and CH2Cl2. Via modification with sodium alginate (AA)...

Summary The influence of oxygen level on brGDGT-based proxies was evaluated by studying GDGTs in three soil profiles with contrasting oxygen level.

Glycerol Dialkyl Glycerol Tetraethers (GDGTs) serve as important tools for the quantitative reconstruction of paleoclimate and paleoecology in both continental and marine environments. Previous studies of GDGTs in the terrestrial environments focused primarily on the soils from the relatively warm-humid or cold-dry regions. However, it is still unclear how GDGTs respond to environmental variables in the cold-humid regions. Here, we collected soils along an altitudinal transect of Mountain (Mt.) Changbai, which has a typical cold-humid climate, to investigate the distribution of GDGTs and the response of GDGT-based proxies to changes in climate along the transect. The shift in the distribution of archaeal isoprenoidal GDGTs (isoGDGTs) revealed that the archaeal community varied significantly along the transect, which can affect the relationship between TEX86 and mean annual air temperature (MAT). In addition, the increased temperature seasonality at higher altitudes exerted a significant impact on TEX86. We proposed a global calibration of TEX86 for the growing season temperature reconstruction in the soil environments: T =85.19×TEX86− 46.30 ( R 2=0.84, p 0.55 are diagnostic for the cold-humid climate. Thus, the combination of MBT′5me and MBT′6me has the potential as a tool for the identification of different types of paleoclimate.

In the process of vehicle collision, the steel material will be deformed by the impact speed. The stress under the same strain will be affected by the change of strain rate. The accuracy of the strain rate curve directly determines the accuracy of the model simulation. This article studies the optimization of material mechanical performance parameters and the correction reprocessing methods of the stress that cannot be obtained by the test in the strain interval. This paper proposes the principle of the modified constitutive equations and the corresponding formula. Based on the approximate model of thin-walled beam under the dynamic impact, the correction coefficient is obtained reversely. While ensuring the accuracy between fitting curve based on the material constitutive equation and the experimental data, the modified constitutive model solves the effect of the non-convergence of stress in a large strain region on the accuracy of the collision simulation model. The dynamic drop weight test results of thin-walled beams show that the modified constitutive equation has great significance for improving the accuracy of simulation models under high-speed impact conditions.

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial membrane lipids that have been extensively used as tools for paleoclimate reconstruction. Temperature and pH were thought to be two major factors affecting the distributions of brGDGTs; however, the effects of other factors on the distribution of brGDGTs and related temperature and pH proxies in soil environments remain unclear. Here, we investigated iso- and br-GDGT distributions in three soil profiles (SPs) developed on bedrocks consisting of hornfels (HP), granite (GP), and basalt (BP), respectively. The downward environmental factors in these SPs differ, thus providing a chance to evaluate their effects on the distribution of brGDGTs. In the three SPs, the methylation degree for 5-methyl and total brGDGTs (MBT′5ME and MBT′), respectively, varied significantly downwards despite minor changes in soil temperature, highlighting a non-temperature effect. The depth-dependence of these proxies appears to be caused by the oxygen level. The MBT′ for 5- or 6-methyl brGDGTs (MBT′5ME and MBT′6ME), or total brGDGTs (MBT′), increased as the oxygen level decreased, suggesting tetramethylated brGDGTs (Ia, Ib, and Ic) would increase in abundance with decreased oxygen level. The two pH proxies, CBT and IR6ME, both decreased at lower oxygen levels. Such regulation of brGDGT compositions in response to oxygen availability could be explained by the changing bacterial communities that have different oxygen preferences. The possible oxygen level impact on the distribution of GDGTs could result in brGDGT-inferred temperature skewed towards higher values and pH towards lower values with decreased oxygen level. This finding may also have implications for the mechanism of soil aridity impact on the brGDGT-based proxies in semi-arid and arid regions, which is of profound importance for paleotemperature and hydroclimate reconstruction in loess-paleosol sequences. Increasing soil aridity could lead to changes in brGDGT-based proxies similar to that observed at the higher oxygen level, i.e., lower MBT′, higher CBT, and higher IR6ME. As soil aridity is generally associated with better aeration and higher oxygen level, we argue that changes in oxygen level might be the real cause of the bias in brGDGT-based proxies in soils from semi-arid and arid regions.

In this paper, flexible Ag electrodes with a hexagonal micromesh structure were fabricated on PET substrate using a photolithography technique. The effect of film thickness on optical and electrical properties of Ag electrodes was investigated systematically. Furthermore, these flexible transparent Ag mesh electrodes were firstly applied to a polymer dispersed liquid crystal (PDLC) device and its performance was evaluated. All of the Ag electrodes exhibited a high average transmittance of about 80.2–85.0% in the visible range (400–800 nm), and the minimum sheet resistance value reached 8.2 Ω sq−1. The prepared Ag mesh also showed an excellent performance of adhesion and bending, demonstrating its superior durability. The PDLC device based on Ag mesh electrodes showed comparable performance with that using ITO electrodes, indicating that the Ag mesh film can be a good substitution for ITO electrodes in PDLC devices and may find practical application in large area flexible devices.

The southeast Qaidam Basin (SQB) lies near the boundary between the modern-day Asian summer monsoon (ASM) and mid-latitude westerly jet, and the paleoclimate variation in this region can be affected by these two atmospheric circulation systems. Reconstructions of paleotemperature and palaeohydrology are therefore critical to constraining the driving forces of climate in this region, where the ecological environment is fragile. Here, we analyzed glycerol dialkyl glycerol tetraethers (GDGTs), microbial membrane lipids occurring ubiquitously in aquatic and terrestrial environments across the globe, in an aeolian sediment profile over the last 7000 years from Xiangride Town (XRD) of southeast Qaidam Basin (SQB), China. The temperature record was generated using the global calibration of MATmr based on branched GDGTs (brGDGTs), whereas the palaeohydrological condition was reconstructed from the relative abundance of isoprenoid GDGTs vs. brGDGTs (Ri/b), the cyclisation index of brGDGTs (CBT), and the brGDGT-based pH indices. The results show that the paleoclimate during the mid-Holocene was relatively warmer and wetter in the SQB. Afterwards it was a trend to a cold and dry climate. Temperature variation was highly coupled with the moisture change during the mid- to late Holocene, as opposed to some previous studies showing a warm-dry and cold-wet climate pattern in the northern Qaidam basin. The palaeohydrological evolution agrees with the precipitation pattern of the Chinese loess plateau but opposes to that in Northeastern China, the middle reaches of Yangtze river and Arid Central Asia (ACA), implying that the ASM strength is the driving force of precipitation evolution during the mid- to late Holocene in the SQB and the spatial heterogeneity of the mid- to late Holocene precipitation pattern across China is remarkable. A rapid cold and drought event at around 4 ka before present (BP) was identified, which might be a key factor that caused the decline in the agricultural civilization during the late Neolithic Age in northwestern China.

We use a recently developed molecular dynamics method with an accurate, first-principles-based force field to study shock propagation in Ni/Al nanolaminates and the induced (highly exothermic) chemical reactions. We characterize both perfect nanolaminates and specimens containing small (4-nm diameter) voids. The new method enables the accurate description of both the nonequilibrium shock-loading process and the long time evolution of the shocked material, providing an atomic-level picture of the complex interplay between the mechanical, thermal, and chemical processes that govern the behavior of the metastable composites. We shock the nanolaminates in the direction normal to the Ni/Al interfaces, leading to multiple wave reflections, due to the elastic mismatch between Ni and Al; this leads to the Al layers having a higher temperature during the early stages of the process. In the perfect nanolaminates, the chemical reactions start at the interfaces closest to the impact plane and then propagate through the material. A rapid increase in the rate of chemical reactions (3Ni + Al → Ni 3 Al) is observed following the melting of the Ni and Al layers. We estimate the propagation velocity of the chemical front to be about 200 m/s. The porous samples exhibit much faster energy-release rates, due to the mechanical intermixing of Al and Ni caused by shock-induced pore collapse and the higher shock temperatures.

We investigate using molecular dynamics, the tensile failure of single-crystal and nanocrystalline Lennard-Jones solids under uniaxial strain. Stresses are relaxed by plasticity and tensile failure, which are induced via stacking faults, twin planes, void nucleation and growth, and their interactions. Stacking faults and twin planes as well as multiple nanovoids are nucleated at grain boundaries in a nanocrystalline solid. Void formation is characterized by under-coordinated atoms with coordination number ≤ 7, and the critical void size is comparable to a vacancy. For a single crystal, the number of stacking faults and twin planes decreases during failure mostly due to the absorption by nanovoids. In contrast, it increases with strain monotonically for a nanocrystalline solid, where abundant grain boundaries help the nucleation and deter the propagation and absorption of the stacking faults and twin planes, inducing effective dislocation pile-ups at grain boundaries even in the presence of nanovoids.

This article examines the attitudes, motivation and behaviors of Chinese college students towards China Internet censorship, and their utilization of circumvention tools to bypass the government Internet blockage, thereby making free connections with the outside world. The current study is a qualitative study based on in-depth interviews with 12 Chinese college students from different parts of China, who have some experience of using circumvention tools. Drawing upon the Uses and Gratification theory and everyday resistance, it is argued that circumvention tools usage, for Chinese college students, is a practical action to resist China’s sophisticated Internet censorship, by which they perform the “anti-agenda setting”. It is also revealed that circumvention is closely correlated with the students’ sense of civil society, human rights, democracy, and more political participation.

Five chemical and four non-chemical presowing treatments were tested on seeds of three conifers (Larix principis-rupprechtii Mayr, Pinus sylvestris L. var. mongolica Litv, and Pinus tabulaeformis Carr.). By itself, cold stratification with snow for 60 days did not significantly improve the germination percentage over that of soaking the seed in warm water (45 °C) for 12 hours. However, including either one or two dehydration-rehydration cycles after the cold stratification did improve both the percentage and speed of germination of seed from all three species. Soaking seed for 12 hours in various chemicals (KNO3, CaCl2, CuSO4, KMnO4 and GA3) before germination was less effective than the snow stratification followed by double dehydration-rehydration treatments (Chang and Lin, 1989).

We demonstrate that shock-induced melting can play a key role in accelerating the initiation and propagation of self-sustained exothermic alloying reactions in nanostructured $\mathrm{Ni}∕\mathrm{Al}$ nanolaminates. Following a pronounced increase of the local pressure upon melting, due to structural expansion, enhanced material diffusion and intermixing around the molten regions accelerate self-sustained alloying reactions, leading to a pressure decrease. This competition between melting and alloying reactions leads to an oscillatory overall pressure as the melting and alloy formation fronts propagate.

We use a recently developed molecular dynamics method with an accurate, first-principles-based force field to study shock propagation in $\mathrm{Ni}∕\mathrm{Al}$ nanolaminates and the induced (highly exothermic) chemical reactions. We characterize both perfect nanolaminates and specimens containing small ($4\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ diameter) voids. This method enables the accurate description of both the nonequilibrium shock loading process and the long-time evolution of the shocked material, providing an atomic-level picture of the complex interplay between the mechanical, thermal, and chemical processes that govern the behavior of the metastable composites. We shock the nanolaminates in the direction normal to the $\mathrm{Ni}∕\mathrm{Al}$ interfaces, leading to multiple wave reflections due to the elastic mismatch between Ni and Al; this leads to the Al layers having a higher temperature during the early stages of the process. In the perfect nanolaminates, the chemical reactions start at the interfaces closest to the impact plane and then propagate through the material. A rapid increase in the rate of chemical reactions $(3\mathrm{Ni}+\mathrm{Al}\ensuremath{\rightarrow}{\mathrm{Ni}}_{3}\mathrm{Al})$ is observed following the melting of the Ni and Al layers. We estimate the propagation velocity of the chemical front to be about $200\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$. The porous samples exhibit much faster energy release rates due to the mechanical intermixing of Al and Ni caused by shock-induced pore collapse and higher shock temperatures.

We employ molecular dynamics simulations with a first principles-based many body potential to characterize the exothermic alloying reactions of nanostructured Ni∕Al multilayers induced by shock loading. We introduce a novel technique that captures both the initial shock transit as well as the subsequent longer-time-scale Ni3Al alloy formation. Initially, the softer Al layers are shock heated to a higher temperature than the harder Ni layers as a result of a series of shock reflections from the impedance-mismatched interfaces. Once initiated, the highly exothermic alloying reactions can propagate in a self-sustained manner by mass and thermal diffusion. We also characterize the role of voids on the initiation of alloying. The interaction of the shock wave with the voids leads not only to significant local heating (hot spots) but also directly aids the intermixing between Al and Ni; both of these phenomena contribute to a significant acceleration of the alloying reactions.

We employ molecular dynamics simulations to characterize the chemical and mechanical response of nanostructured Ni/Al multilayers induced by shock loading, using a novel technique that captures both the initial shock transit as well as the subsequent longer‐timescale chemical processes. Initially, the softer Al layers are shock‐heated to a higher temperature than the harder Ni layers, as a result of a series of shock reflections from the impedance‐mismatched interfaces. Once initiated, the highly exothermic alloying reactions can propagate in a self‐sustained manner by mass and thermal diffusion.

We identify a shock-induced melting and great facilities of the melting in accelerating subsequent alloying reactions in nanostructured Ni/Al multilayer films using a novel molecular dynamics technique, which captures the initial shock transit as well as the subsequent long time scale alloying process. We observe a pronounced increase of the pressure in the melting process (i.e., a process of coexistence of solid and liquid phases). As soon as the melting completes, the temperature increases dramatically indicating a start of explosive alloying reactions and the pressure starts to decrease. The pressure going up or down is determined by the competition between melting and alloying reactions.