•We do image classification on training data limited dataset with deep learning.•Transfer learning is employed to overcome the serious over-fitting.•Web data augmentation is developed to improve the ...classification performance.•Bayesian optimization is employed to facilitate the hyper-parameter search.
Since Convolutional Neural Network (CNN) won the image classification competition 202 (ILSVRC12), a lot of attention has been paid to deep layer CNN study. The success of CNN is attributed to its superior multi-scale high-level image representations as opposed to hand-engineering low-level features. However, estimating millions of parameters of a deep CNN requires a large number of annotated samples, which currently prevents many superior deep CNNs (such as AlexNet, VGG, ResNet) being applied to problems with limited training data. To address this problem, a novel two-phase method combining CNN transfer learning and web data augmentation is proposed. With our method, the useful feature presentation of pre-trained network can be efficiently transferred to target task, and the original dataset can be augmented with the most valuable Internet images for classification. Our method not only greatly reduces the requirement of a large training data, but also effectively expand the training dataset. Both of method features contribute to the considerable over-fitting reduction of deep CNNs on small dataset. In addition, we successfully apply Bayesian optimization to solve the tuff problem, hyper-parameter tuning, in network fine-tuning. Our solution is applied to six public small datasets. Extensive experiments show that, comparing to traditional methods, our solution can assist the popular deep CNNs to achieve better performance. Particularly, ResNet can outperform all the state-of-the-art models on six small datasets. The experiment results prove that the proposed solution will be the great tool for dealing with practice problems which are related to use deep CNNs on small dataset.
Polymer‐based solid electrolytes (PSEs) have attracted tremendous interests for the next‐generation lithium batteries in terms of high safety and energy density along with good flexibility. ...Remarkable performances have been demonstrated in PSEs, which endowed PSEs with the potential to replace liquid electrolytes to meet the market demands. In this review, polymer matrices, different polymer architectures, and functional filler materials used in PSEs are discussed to explore the design concepts, methodologies, working mechanisms, and pros and cons of various PSEs. In addition, their recent notable applications in all‐solid‐state lithium ion batteries, lithium–sulfur batteries, suppression of lithium dendrites, and flexible lithium batteries are also introduced. Finally, the challenges and future prospects are sketched to provide strategies to explore novel PSEs for high‐performance all‐solid‐state lithium batteries.
Polymer‐based solid electrolytes (PSEs) have the potential to replace liquid electrolytes to realize all‐solid‐state lithium batteries with high safety. This review summarizes some recent prominent advancements in PSEs with regards to polymer matrix selection, architectural engineering of polymers, and properties of different fillers. Application of PSEs in lithium batteries, suppression of lithium dendrites, and flexible batteries are also highlighted.
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•Seawater intrusion researches were evaluated in a verifiable and repeatable manner.•Research situation, global study areas and hot topics were identified and explained.•Research ...directions and potential breakthrough were summarized and classified.
Seawater intrusion (SWI) is becoming one of the major environmental issues in more and more coastal areas around the world. Understanding the current SWI situation and forming research consensus are of great significance for further studies and coastal water resources management. In this study, we analyzed the SWI-associated literature available from the Science of Citation Index Expanded (SCIE) bibliographic database by using CiteSpace to further excavate existing research achievement. We explored a new method for identifying global geographic distributions of 501 coastal cities where SWI has been reported. It can be found that SWI is more likely to occur in well-recharged major basins (recharge rate 100–300 mm/a) or local shallow aquifers with high population density. According to current reports, about 32% of the coastal metropolitan cities (population > 1 million within 150 km from coastline) have been threatened. There was a 20-fold increase rate in the number of papers related to SWI compared to that in general science and technology. The United States of America, China, Australia were the top 3 contributors in SWI scope, contributed 46.4% of the total number of articles. More than 600 researches were supported by Chinese funds, which made China become the second contributor. But the number of citations per Chinese article was the lowest among the top 10 contributors. By co-citation analysis, we identified top 5% articles, and elaborated the background knowledge by taking Top 10 co-cited articles as example. A series of keywords with high co-occurrence were identified. Their meanings and relations were stated and graphically illustrated. As a keyword, SWI frequently appears in the following five research directions: analysis of the location or morphology of fresh and salt water interface, the prediction of groundwater quality, the geothermal circulation and tectonic activities, the coastal mangrove wetlands protection, and the management of water resources in coastal zones. We critically evaluated the bibliometric results and reviewed future opportunities and challenges for this field. With the development of new technology and the accumulation, the improvement of coastal environment will certainly benefit from the study of SWI.
A gas sensor based on the In2O3–rGO nanocomposites was successfully fabricated, which exhibited excellent selectivity, high response, relatively short response and recovery times for detection of NO2 ...at room temperature.
In this paper, well-controlled synthesis of In2O3-reduced graphene oxide (In2O3–rGO) nanocomposites by hydrothermal method was demonstrated. The structural, morphological, chemical composition studies of the In2O3–rGO nanocomposites were carried out, evidencing a homogeneous dispersion of In2O3 on the rGO nanosheets. The sensor based on the In2O3–rGO nanocomposites exhibited excellent selectivity, high response, and relatively short response and recovery time for detection of NO2 at room temperature. The excellent sensing properties were resulted from the composition and structure advantages of the In2O3–rGO nanocomposites.
Metallic Li is considered the most promising anode material for high‐energy density batteries due to its high theoretical capacity and low electrochemical potential. However, commercialization of the ...Li anode has been hampered by the safety issue associated with Li‐dendrite growth resulting from uneven Li‐ion deposition and an unstable solid electrolyte interphase (SEI). Herein, an in situ prepared 10 nm thin film of covalent organic framework (COF) uniformly covered on the Li anode (COF‐Li) is used as an artificial SEI layer for Li plating/striping stabilization and Li dendrite inhibition. Abundant microcellular structures in the COF can redistribute the Li‐ion flux and lead to the homogeneous plating/stripping process. Meanwhile, the superhard mechanical properties and mechanical behavior during needling of the ultrathin COF film is studied via the digital pulsed force mode equipped in atomic force microscopy, illustrating a high Young's modulus of 6.8 GPa that is strong enough to resist dendrite growth. As a result, stable cycling for 400 h is achieved in the COF‐Li symmetrical cell at a current density of 1 mA cm−2, and the internal short circuit is effectively blocked by COF‐Li in Li–S batteries.
Thin and rigid covalent organic framework films as an artificial solid electrolyte interphase for Li metal anodes not only redistributes the Li‐ion flux, reduces the side reactions between Li metal and electrolytes, and leads to the homogeneous plating/stripping process, but also strongly represses dendrite formation on the Li anode and exposure to ensure battery safety.
China's Central government has released an ambitious plan to tackle the nation's water pollution crisis. However, this is inhibited by a lack of data, particularly for groundwater. We compiled and ...analyzed water quality classification data from publicly available government sources, further revealing the scale and extent of the crisis. We also compiled nitrate data in shallow and deep groundwater from a range of literature sources, covering 52 of China's groundwater systems; the most comprehensive national-scale assessment yet. Nitrate pollution at levels exceeding the US EPA's maximum contaminant level (10 mg/L NO3N) occurs at the 90th percentile in 25 of 36 shallow aquifers and 10 out of 37 deep or karst aquifers. Isotopic compositions of groundwater nitrate (δ15N and δ18ONO3 values ranging from −14.9‰ to 35.5‰ and −8.1‰ to 51.0‰, respectively) indicate many nitrate sources including soil nitrogen, agricultural fertilizers, untreated wastewater and/or manure, and locally show evidence of de-nitrification. From these data, it is clear that contaminated groundwater is ubiquitous in deep aquifers as well as shallow groundwater (and surface water). Deep aquifers contain water recharged tens of thousands of years before present, long before widespread anthropogenic nitrate contamination. This groundwater has therefore likely been contaminated due to rapid bypass flow along wells or other conduits. Addressing the issue of well condition is urgently needed to stop further pollution of China's deep aquifers, which are some of China's most important drinking water sources. China's new 10-point Water Pollution Plan addresses previous shortcomings, however, control and remediation of deep groundwater pollution will take decades of sustained effort.
•China's official groundwater and surface water quality classification data reviewed.•Compilation of literature groundwater nitrate data reveals endemic pollution.•Deep groundwater pollution widespread, pointing to major well integrity problems.•Ten-point water pollution plan addresses previous barriers, but not all mechanisms.
Sharing the use of a bicycle in China has changed people's daily travel modes. Existing studies mainly explored the factors affecting individuals' initial intentions to start using a shared bicycle, ...but few looked at the likelihood that a user would continue using one. Based on a post-acceptance model of information system (IS) continuance, this investigation proposed a research model to investigate factors influencing riders' intentions to continued usage of shared bikes. Analysis involved structural equation modeling (SEM) and fuzzy-set qualitative comparative analysis (fsQCA) on data from 376 shared bicycle riders. The results from SEM showed that perceived usefulness, service quality, riders' habits, overall satisfaction and the nature of the weather were the most important factors positively influencing users' intentions to continue bike sharing. The results from fsQCA showed that six combinations of these variables were sufficient to explain continued usage. The conclusions of this study can be useful for operators to improve shared bicycle services.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Proton exchange membranes (PEMs) have received immense attentions for their core roles in high temperature proton exchange membrane fuel cells (HT-PEMFCs). For a high-performance polymer electrolyte, ...stable mechanical property and high proton conductivity on the order of 10−2 S cm−1 at low humidity (or anhydrous conditions) and high temperature are ultimately necessary. With emphasis on this practical principle, phosphoric acid doped polybenzimidazoles (PBIs) have become one of the hottest materials in the field of proton conducting membrane that exhibit high proton conductivity with values closing to 10−2 S cm−1. In addition to PBI, non-PBI based proton conducting polymers that exhibit satisfactory conductivity and intrinsic mechanical stability are also exciting research in HT-PEMs. This review summarizes the recent progresses in the HT-PEMs, and addresses the challenges and promising directions for further development of HT-PEMs.
•Influences of structure for membrane on single cell performance are analyzed.•Four categories of high temperature proton exchange membranes are summarized.•Advantages and drawbacks for proton exchange membranes are contrasted.•Suggestions of future development for proton exchange membranes are discussed.
•Effects of porewater in aquitards on aquifer groundwater quality are investigated.•Aqueous extraction (AE) & squeezing (SE) methods were used to get porewater chemistry.•The primary source of ...solutes might be different in the central and coastal profiles.•Release of constituents from aquitards is driving degradation of groundwater quality.•Significant storage of porewater solutes is within low permeability sediments.
Groundwater interacts with porewater within clay-rich sequences. However, the effects of aquitard porewater on groundwater quality are generally poorly understood. This study explores potential links between porewater chemistry in a thick clay-rich sequence of Quaternary sediments, and groundwater quality in the North China Plain (NCP), one of China’s most important water supply aquifers. Previous studies have hypothesised the release of salinity, fluoride, and sulphate from aquitards in response to intensive pumping, without explicitly analysing the chemistry of aquitard porewaters. This study further investigated this hypothesis through targeted analysis of porewater chemistry profiles through the NCP sedimentary sequence. Two cores were analysed – one in the central plain (Hengshui, HS) and the other in the coastal plain (Cangzhou, CZ). Both areas have experienced significant groundwater extraction over recent decades from confined aquifers inter-layered with clays. Aqueous extraction (AE) and squeezing (SE) methods were both used to assess porewater chemistry. The hydrochemical characteristics of groundwater are closer to those of the squeezed porewater, which can be regarded as more closely corresponding to in-situ porewater compositions than AE profiles. Chloride was generally consistent between the two methods, while sulphate and fluoride concentrations were greater using AE, ranging from 340 to 48,700 mg/L and 8.8 to 144 mg/L, compared to 350 to 8860 mg/L and 0.2 to 4.3 mg/L using SE, respectively. The much greater concentrations of fluoride derived from the AE method indicates a high susceptibility to release during changes to the ambient geochemical environment. While the primary fluoride sources in groundwater and porewater are likely minerals from weathering of volcanic rocks in the sedimentary sequence, release into groundwater appears linked to common geochemical influences such as high Na/Ca ratio (increased during cation exchange) and the presence of iron and aluminium oxides (providing sorption sites). The primary source of solutes is interpreted to be different in each profile, with evapotranspiration important in the central plain and marine solutes important in the coastal profile, indicating significant storage of salinity, fluoride, and sulphate within low permeability sediments. Our data supports the hypothesis that release of these ions is driving degradation of groundwater quality, in response to decades of intensive groundwater extraction, which is an ongoing threat to the quality of groundwater in the NCP.
•Impacts of anthropogenic landscape change on groundwater recharge (GR) reviewed.•Agricultural and urban land conversion affect GR rates, locations and mechanisms.•Combination of tracer, physical and ...modelling techniques can be employed.•Quantifying effects of urbanisation on GR presents a major research challenge.
The impacts of anthropogenic modifications to the landscape on groundwater recharge rates, locations, and mechanisms are reviewed. The two major categories of change examined are conversion of land for agriculture and urbanization, both of which have significant effects on groundwater recharge. Techniques for identifying and quantifying the changes in recharge due to these impacts are discussed. Land-clearing for agriculture and surface water transfer for irrigation have resulted in order of magnitude increases in recharge rates in many semi-arid regions worldwide, causing ongoing land and water salinization and water-logging problems. While increased recharge by irrigation return flow may alleviate shallow groundwater depletion in some settings, this is complicated by the effect of unsaturated zone thickening, which reduces the fraction of potential recharge becoming actual recharge, and may result in new water quality risks such as nitrate contamination. Expansion of urban and peri-urban land and their associated surface and sub-surface infrastructure results in complex water balance changes that re-distribute groundwater recharge locations, modify recharge mechanism(s) and result in variable impacts on recharge rates (e.g., overall net decrease, increase or minimal change) and quality. While changes to groundwater recharge resulting from conversion of land for agriculture are relatively well understood, less is documented about the changes resulting from urbanization, due to a paucity of data from field-based studies. Two case studies from Beijing, China and Melbourne Australia are examined, which highlight these impacts and demonstrate some potential methodological techniques for this topic.
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