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Hypothesis The self-assembly of amphiphilic molecules onto solid substrates can result both in the formation of monolayers and multilayers. However, on oxidized and non-oxidized copper (Cu), only monolayer formation was reported for phosphonic acids possessing one phosphate head group. Here, the adsorption of octadecylphosphonic acid (ODPA) on Cu substrates through a self-assembly process was investigated with the initial hypothesis of monolayer formation. Experiments The relative amount of ODPA adsorbed on a Cu substrate was determined by infrared reflection/absorption spectroscopy (IRRAS) and by atomic force microscopy (AFM) investigations before and after ODPA deposition. X-ray photoelectron spectroscopy (XPS) with sputtering was used to characterize the nature of the layers. Findings The results show that the thickness of the ODPA layer increased with deposition time, and after 1 h a multilayer film with a thickness of some tens of nm was formed. The film was robust and required long-time sonication for removal. The origin of the film robustness was attributed to the release of Cu ions, resulting in the formation of Cu-ODPA complexes with Cu ions in the form of Cu(I). Preadsorbing a monolayer of octadecylthiol (ODT) onto the Cu resulted in no ODPA adsorption, since the release of Cu(I) ions was abolished.

Two-dimensional (2D) van der Waals heterostructures have attracted enormous research interests due to their emergent electrical and optical properties. The comprehensive understanding and efficient control of interlayer couplings in such devices are crucial for realizing their functionalities, as well as for improving their performance. Here, we report a successful manipulation of interlayer charge transfer between 2D materials by varying different stacking layers consisting of graphene, hexagonal boron nitride, and tungsten disulfide. Under visible-light excitation, despite being separated by few-layer boron nitride, the graphene and tungsten disulfide exhibit clear modulation of their doping level, i.e., a change of the Fermi level in graphene as large as 120 meV and a net electron accumulation in WS2. By using a combination of micro-Raman and photoluminescence spectroscopy, we demonstrate that the modulation is originated from simultaneous manipulation of charge and/or energy transfer between each of the two adjacent layers. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version

Fundamental understandings on the dynamics of charge carriers and excitonic quasiparticles in semiconductors are of central importance for both many-body physics and promising optoelectronic and photonic applications. Here, we investigated the carrier dynamics and many-body interactions in two-dimensional (2D) transition metal dichalcogenides (TMDs), using monolayer WS2 as an example, by employing femtosecond broadband pump-probe spectroscopy. Three time regimes for the exciton energy renormalization are unambiguously revealed with a distinct red-blue-red shift upon above-bandgap optical excitations. We attribute the dominant physical process in the three typical regimes to free carrier screening effect, Coulombic exciton–exciton interactions and Auger photocarrier generation, respectively, which show distinct dependence on the optical excitation wavelength, pump fluences and/or lattice temperature. An intrinsic exciton radiative lifetime of about 1.2 picoseconds (ps) in monolayer WS2 is unraveled at low temperature, and surprisingly the efficient Auger nonradiative decay of both bright and dark excitons puts the system in a nonequilibrium state at the nanosecond timescale. In addition, the dynamics of trions at low temperature is observed to be significantly different from that of excitons, e.g., a long radiative lifetime of ~ 108.7 ps at low excitation densities and the evolution of trion energy as a function of delay times. Our findings elucidate the dynamics of excitonic quasiparticles and the intricate many-body physics in 2D semiconductors, underpinning the future development of photonics, valleytronics and optoelectronics based on 2D semiconductors. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Deep neural network has been adopted as the standard model to predict ads click-through rate (CTR) for commercial online advertising systems. Deploying an industrial scale ads system requires to overcome numerous challenges, e.g., hundreds or thousands of billions of input features and also hundreds of billions of training samples, which under the cost budget can cause fundamental issues on storage, communication, or the model training speed. In this work, we present Baidu's industrial-scale practices on how to apply the system and machine learning techniques to address these issues and increase the revenue. In particular, we focus on the strategy for developing GPU-based CTR models combined with quantization techniques to build a compact and agile system which noticeably improves the revenue. With quantization, we are able to effectively increase the model (embedding layer) size without increasing the storage cost. This brings an increase in prediction accuracy and yields a 1% revenue increase and 1.8% higher relative click-through rate in the real sponsored search production environment.

The rapid advances of nanotechnology and nanophotonics bring new approaches for manipulating light–matter interactions at the nanoscale, for example, by integrating plasmonic nanostructures with two-dimensional transition metal dichalcogenides (TMDs) to achieve strong exciton–plasmon interactions for applications in optical switches, sensing, and photovoltaic devices. Such a TMD-plasmonic coupled system provides a highly unexplored territory toward understanding the exciton–plasmon interactions for ultrafast operations. Utilizing transient absorption pump–probe spectroscopy, here we report an ultrafast modulation of the exciton–plasmon coupling in a monolayer WS2–Ag nanodisk hybrid system that displays Fano resonance at the steady-state regime. Specifically, the instant switch-off of the Fano resonance was observed upon the femtosecond pump excitation, characterized by the photoinduced absorption signal at the Fano resonance frequency. The fast recovery of the Fano resonance starts at the sub-100 fs time scale as a result of the energy transfer from excitons of WS2 to plasmons in Ag nanodisks. The slow recovery lasts for several tens of picoseconds, following the carrier relaxations in the subsystems. The ultrafast modulation of the exciton–plasmon coupling in the integrated TMD–plasmonic hybrid system will offer new opportunities for technologically relevant high-speed active plasmonic devices. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

The Chinese lunar probe Chang'e-4 (CE-4) landed in the Von Kármán crater within the South Pole–Aitken (SPA) basin on the far-side of the Moon on 3 January 2019. Following this, the moon rover Yutu-2 separated from the CE-4 lander and started its travels and exploration on the far-side of the Moon. Before this landing, humans had remotely observed the far-side of the Moon with lunar satellites. However, it was the first time that a man-made spacecraft had landed there and actually left behind wheel prints belonging to humanity. Since China's Lunar Exploration Project (CLEP), or Chang'e Project, started in 2004, China has accomplished the first two steps of its three-step plan of ‘Orbiting, Landing and Returning’. CE-3 and CE-4 landed successfully on the near-side and far-side of the Moon, respectively. In the near future, CE-5 will land again on the near-side of the Moon and take lunar rock and soil samples back to Earth, thus completing the three-step plan of CLEP. In April 2019, National Science Review (NSR) interviewed three key figures of CLEP: CLEP Chief Engineer Weiren Wu (), the first CLEP Chief Scientist and CLEP senior consultant Ziyuan Ouyang (), and CLEP third phase Vice-Chief Engineer, CE-4 Ground Research and Application System Director Chunlai Li (). They talked about the scientific expectations and future plans of China's lunar and deep space exploration.

In this perspective article, the novel technique "nano infrared microscopy" is introduced as a valuable tool in the field of corrosion science to obtain chemical information with a spatial resoluti ...

The selaginellin derivatives are a type of novel natural pigments with an unusual alkynyl phenol skeleton from the genus Selaginella. Some of these natural compounds were previously reported to show important bioactivities, including anticancer activity, cardiovascular protection and phosphodiesterase-4 inhibition. We designed and synthesized fifteen biphenyl-containing diaryl acetylene derivatives mimicking the skeleton of natural alkynyl phenols. In MTT assay in cancer cells, compounds 1c, 2d, 2g, 2h, 2i and 2j exhibited potent antiproliferative activity. The evaluation of Hypoxia Inducible Factor-1 (HIF-1) pathway inhibitory activity in dual luciferase assay demonstrated that most tested compounds exhibited moderate to good activities. Compounds 1a, 2f and 2h displayed high HIF-1 inhibitory activities and relatively low cytotoxicity, demonstrating great potential as HIF-1 inhibitors. These results afford a new strategy for the discovery of new HIF-1 inhibitors and anti-proliferative agents from natural or synthetic diaryl acetylene derivatives.

The National Natural Science Foundation of China (NSFC) is the major funding agency for China's basic research in natural science. The total budget for NSFC was 26.7 billion Yuan (RMB) in 2017, accounting for 27% of China's total investment in basic research. In the past decades, continuous increases in the National Natural Science Fund and other funding programs provided strong support for the rapid growth in China's science and technology (S&T). In the second half of 2018, NSFC unveiled a deep reform plan that aims to build a fair, efficient and standardized new funding system that meets the demands of excellence in science in the twenty-first century in 5–10 years. Why did NSFC propose this reform? What are the major tasks of this reform? And how would NSFC implement this reform? All-in-all, this reform would not only have profound effect on S&T in China but also matters the world for the global collaborative efforts for the science. Recently, National Science Review had an exclusive interview with Jinghai Li, President of NSFC and Academician of the Chinese Academy of Sciences, to learn his views and perspectives of the future of NSFC.

Atomically thin transition metal dichalcogenides possess valley dependent functionalities that are usually available only at crogenic temperatures, constrained by various valley depolarization scatterings. The formation of exciton polaritons by coherently superimposing excitons and microcavity photons potentially harnesses the valley polarized polariton polariton interactions for novel valleytronics devices. Robust EPs have been demonstrated at room temperature in TMDs microcavity, however, the coherent polariton lasing and condensation remain elusive. Herein, we demonstrate for the first time the realization of EP condensation in a TMD microcavity at room temperature. The continuous wave pumped EP condensation and lasing with ultralow thresholdsis evidenced by the macroscopic occupation of the ground state, that undergoes a nonlinear increase of the emission and a continuous blueshift, a build up of spatial coherence, and a detuning-controlled threshold. Our work presents a critically important step towards exploiting nonlinear polariton polariton interactions and polaritonic devices with valley functionality at room temperature., Comment: 21 pages, 5 figures

This paper investigates a dual-channel supply chain in which a manufacturer sells the product via an offline retailer or online store. The manufacturer sets the wholesale and online price, and the retailer decides the retail price with the retailer’s fairness preference and consumer’s online channel preference. Through investigating the combined impacts of fairness preference and channel preference on the enterprises’ operational strategies, this paper obtains some meaningful results. If a manufacturer thinks over the fairness preference, he decreases the wholesale price to mitigate a loss of retailer and benefit the supply chain design. The manufacturer intends to set up the online channel with a lower acceptance as the fairness preference grows. However, the gains from enhanced online channel acceptance cannot compensate for the manufacturer’s loss by the fairness effect that benefits the retailer. Moreover, the manufacturer cannot neglect the retailer’s fairness preference generating a “lose-lose” case for both members.

All-inorganic metal halides perovskites (CsPbX3, X = Br or Cl) show strong excitonic and spin-orbital coupling effects, underpinning spin-selective excitonic transitions and therefore exhibiting great promise for spintronics and quantum-optics applications. Here we report spin-dependent optical nonlinearities in CsPbX3 single crystals by using ultrafast pump-probe spectroscopy. Many-body interactions between spin-polarized excitons act like a pseudo-magnetic field and thus lift the degeneracy of spin states resulting in a photoinduced circular dichroism. Such spontaneous spin splitting between “spin-up” and “spin-down” excitons can be several tens of milli-electron volts under intense excitations. The exciton spin relaxation time is ~20 picoseconds at very low pump fluence, the longest reported in the metal halides perovskites family at room temperature. The dominant spin-flip mechanism is attributed to the electron-hole exchange interactions. Our results provide essential understandings towards realizing practical spintronics applications of perovskite semiconductors., Strong excitonic effects and spin-orbit coupling in all-inorganic halide perovskite is promising for spintronic application, yet the spin-dependent phenomenon is not well understood. Here, the authors reveal that many-body interactions between spin-polarized excitons act like pseudo-magnetic field, lifting the degeneracy and resulting in circular dichroism.

The COVID-19 pandemic has killed more than 1 000 000 people within nine months in 2020. The world is changed as the cities were locked down, the traffic reduced, and people forced to work from home and keep social distance. These controlling measures also resulted in drastic reduction of the emission of many air pollutants, providing researchers an unprecedented large-scale natural experiment in examining how the air quality would respond to a strong forcing. In this panel discussion held on 22 September 2020, five experts gathered to discuss their observations and analyses, as well as the current understanding and misconception about airborne transmission. This Forum article is dedicated to Prof. Martin Williams of the Imperial College London, who intended to join the panel discussion but passed away one day before it. Guy Brasseur Professor of Max Planck Institute for Meteorology, Germany Junji Cao Professor of Institute of Earth Environment, Chinese Academy of Sciences, China Aijun Ding Dean and Professor of School of Atmospheric Sciences, Nanjing University, China Lidia Morawska Professor of Queensland University of Technology, Australia Tong Zhu (Chair) Dean and Professor of College of Environmental Sciences and Engineering, Peking University, China

Hepatoprotectant is critical for the treatment of liver disease. This study first reported the application of a liver chip in the hepatoprotective effect assessment. We first established a biomimetic sinusoid-on-a-chip by laminating four types of hepatic cell lines (HepG2, HUVEC, LX-2, and U937 cells) in a single microchannel with the help of laminar flow in the microchannel and some micro-fences. This chip was straightforward to fabricate and operate and was able to be long-term cultured. It also demonstrated better hepatic activity (cell viability, albumin synthesis, urea secretion, and cytochrome P450 enzyme activities) over the traditional planar cell culture model. Then, we loaded three hepatoprotectants (tiopronin, bifendatatum, and glycyrrhizinate) into the chip followed by the addition of acetaminophen as a toxin. We successfully observed the hepatoprotective effect of these hepatoprotectants in the chip, and we also found that bifendatatum predominantly reduced alanine transaminase secretion, tiopronin predominantly reduced lactate dehydrogenase secretion, and glycyrrhizinate predominantly reduced aspartate transaminase secretion, which revealed the different mechanisms of these hepatoprotectants and provided a clue for following molecular biological study of the protecting mechanism.

The year of 2020 has been overshadowed by the COVID-19 pandemic. Medical workers throughout China have played critical roles in battling severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) and saving lives. The whole of society has now fully realized the significance of medical workers and many began to think about medical education in China: How can we further improve medical education for the next generation of clinicians, medical scientists, nurses, public-health workers and administrators related to medical care, so that they are well prepared to meet societal needs for medical care in the ever-changing world? In this panel discussion, medical-education experts from several prominent medical schools in China gathered to discuss the reform and future development of China's medical education. Xiang Chen President of Xiangya School of Medicine, Vice President of Central South University, Changsha, China Baorong Chi Professor of Norman Bethune Health Science Center of Jilin University, Changchun, China Yiqun Hu Vice Chancellor of Shanghai Jiao Tong University School of Medicine, Shanghai, China Yang Ke Professor of Peking University Health Science Center, former Vice President of Peking University, Beijing, China Ming Kuang Vice President of Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, China Mengfeng Li President of Southern Medical University, Guangzhou, China Hongbing Shen President of Nanjing Medical University, Nanjing, China Xuehong Wan Professor of West China Medical Center, Vice President of Graduate School of Sichuan University, Chengdu, China Hong Yan President of Xi’an Jiaotong University Health Science Center, Vice President of Xi’an Jiaotong University, Xi’an, China Guoqiang Chen (Chair) Chancellor of Shanghai Jiao Tong University School of Medicine, Vice President of Shanghai Jiao Tong University, Shanghai, China

Approximate nearest neighbor (ANN) searching is a fundamental problem in computer science with numerous applications in (e.g.,) machine learning and data mining. Recent studies show that graph-based ANN methods often outperform other types of ANN algorithms. For typical graph-based methods, the searching algorithm is executed iteratively and the execution dependency prohibits GPU adaptations. In this paper, we present a novel framework that decouples the searching on graph algorithm into 3 stages, in order to parallel the performance-crucial distance computation. Furthermore, to obtain better parallelism on GPU, we propose novel ANN-specific optimization methods that eliminate dynamic GPU memory allocations and trade computations for less GPU memory consumption. The proposed system is empirically compared against HNSW–the state-of-the-art ANN method on CPU–and Faiss–the popular GPU-accelerated ANN platform–on 6 datasets. The results confirm the effectiveness: SONG has around 50-180x speedup compared with single-thread HNSW, while it substantially outperforms Faiss.

Photodynamic therapy (PDT) is a non-invasive and innovative therapeutic approach which has been increasingly applied in clinical cancer therapy. As the central element of PDT, the development of novel photosensitizers (PSs) with longer absorption wavelength, proper lipophilic/hydrophilic profiles, target tissue selectivity, and higher photo-/lowest dark-cytotoxicity is a challenging task. Previously, we designed and synthesized a series of novel long-wavelength chlorin e6 (Ce6)-based PSs via introducing aromatic groups to the vinyl of Ce6 skeleton. The new formed compounds with π-extension system exhibited improved photodynamic effects and spectral characteristics. Among these π-conjugated chlorin PSs, (E)-32-(4-methoxyphenyl)-chlorin e6, named A15, was expected to be a potent antitumor candidate as a PDT agent due to its good photobiological properties. Herein, in this work, we evaluated the effectiveness of A15 in cancer PDT. In vitro, a novel rare earth probe, ATTA-Eu3+ was applied to detect the singlet oxygen (1O2) production of A15 in solution and human hepatoma HepG2 cells, respectively. Moreover, A15 exhibited strong phototoxicity and weak dark cytotoxity to HepG2 cells. In H22 tumor bearing mice, A15 showed excellent tumor accumulation ability via i.v. administration and induced tumor regression, followed by laser treatment. These results indicated that A15 is a potential novel π-extension chlorin-type PS for PDT applications.

It has been more than 10 years since Satoshi Nakamoto published his famous paper entitled ‘Bitcoin: a peer-to-peer electronic cash system’, which set the foundation of blockchain technology. Accompanied by the price volatility of bitcoins from 2017 to 2018, blockchain has been a hot word on the internet, and particularly hot in China. Blockchain offers a distributed and secure system for data storage and value transactions. Its applications are springing up in multiple fields. The Chinese government is considering these trends with great caution. Initial coin offering has been banned in China since September 2017. By contrast, an official white paper on China's blockchain technology, which was released in May 2018, said that blockchain technology will be widely applied in the real economy of China within 3 years. In a recent panel discussion held by National Science Review, experts talked about related topics. Their opinions may provide a quick view of the future development of blockchain in China and abroad. Jing Chen Assistant Professor of Computer Science Department, Stony Brook University and Chief Scientist at Algorand LLC, USA Xiaotie Deng Professor of School of Electronics Engineering and Computer Science, Peking University, China Guohua Gan Vice President of Beijing Tai Cloud Technology Corp., China Xiaoyun Wang Professor of Institute of Advanced Study, Tsinghua University, China Zhiming Zheng Professor of School of Mathematics and Systems Science, Beihang University, China Lei Guo (Chair) Professor of Academy of Mathematics and Systems Science, Chinese Academy of Sciences, China

The 1D Ag3PO4 sensitized SrTiO3 nanowires are prepared by simple route of electrospinning-in situ deposition technique. The results of the thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive Spectrometer (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–Visible diffuse reflectance spectroscopy (UV–Vis) indicate that the Ag3PO4 nanoparticles has been deposited on the surface of the SrTiO3 nanowires successfully. Experimental results showed that compared with pure SrTiO3, the as-prepared 1D Ag3PO4 sensitized SrTiO3 nanowires exhibit obvious enhancement of photocatalytic performance and stability. Especially, the Ag3PO4/SrTiO3 (3AS sample) had a satisfactory photocatalytic activity for degrading methylene blue (MB) more than 98% under visible light irradiation. As to pure SrTiO3 and Ag3PO4, only 9.8% and 49% of MB was decomposed after 35 min irradiation respectively. Furthermore, the mechanism of the enhancing photocatalytic activity could be ascribed to the nano-heterojunction of the Ag3PO4/SrTiO3, the visible light response of the Ag3PO4, and the 1D structure of the nanowires.

Metal halide perovskite materials are an emerging class of solution-processable semiconductors with considerable potential for use in optoelectronic devices1–3. For example, light-emitting diodes (LEDs) based on these materials could see application in flat-panel displays and solid-state lighting, owing to their potential to be made at low cost via facile solution processing, and could provide tunable colours and narrow emission line widths at high photoluminescence quantum yields4–8. However, the highest reported external quantum efficiencies of green- and red-light-emitting perovskite LEDs are around 14 per cent7,9 and 12 per cent8, respectively—still well behind the performance of organic LEDs10–12 and inorganic quantum dot LEDs13. Here we describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20 per cent. This achievement stems from a new strategy for managing the compositional distribution in the device—an approach that simultaneously provides high luminescence and balanced charge injection. Specifically, we mixed a presynthesized CsPbBr3 perovskite with a MABr additive (where MA is CH3NH3), the differing solubilities of which yield sequential crystallization into a CsPbBr3/MABr quasi-core/shell structure. The MABr shell passivates the nonradiative defects that would otherwise be present in CsPbBr3 crystals, boosting the photoluminescence quantum efficiency, while the MABr capping layer enables balanced charge injection. The resulting 20.3 per cent external quantum efficiency represents a substantial step towards the practical application of perovskite LEDs in lighting and display. A strategy for managing the compositional distribution in metal halide perovskite light-emitting diodes enables them to surpass 20% external quantum efficiency—a step towards their practical application in lighting and displays.

A novel magnetic silica gel adsorbent (Fe3O4-Si-COOH) was successfully prepared by introducing carboxyl group in situ to improve the performance for Pb(II), Zn(II), and Cd(II) adsorption. Infrared spectroscopy (IR), scanning electron microscope (SEM), transmission electron microscope (TEM), thermo-gravimetric analyzer (TGA), the Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) characterizations suggested that Fe3O4-Si-COOH has been successfully prepared. The adsorption performance was evaluated by batch experiments with different initial concentrations, ionic strength, contact time, and pH. The adsorption kinetics data followed pseudo-second-order model and exhibited a three-stage intraparticle diffusion mode. Isothermal adsorption equilibrium data were best fitted by the Freundlich model and the adsorption capacity were 155, 110, and 93 mg/g (initial concentration 210 mg/L) for Pb(II), Zn(II), and Cd(II), respectively. The result of X-ray photoelectron spectroscopy (XPS) survey spectrum suggested that the main adsorption mechanism is that the H+ of carboxyl groups exchanged with heavy metal ions in the adsorption processes. In addition, the adsorbed Fe3O4-Si-COOH could be regenerated and the adsorption capacity of reused Fe3O4-Si-COOH could maintain 80.3% after five cycles. Hence, the Fe3O4-Si-COOH could be a kind of potential material for removing Pb(II), Zn(II), and Cd(II) from wastewater.

The 3D Z-scheme Ag3PO4/Ag/MoS2/TiO2 nano-heterojunction is synthesized via electrospinning-hydrothermal-chemical co-deposition method. Compared with the unmodified samples, the photocatalysis of the Ag3PO4/Ag/MoS2/TiO2 nano-heterojunction exhibits a remarkable enhancement by the degradation of methylene blue(MB) in sunlight. Further, the Z-scheme heterojunction is considered as the main reason for the enhancement.

In the foreseeable future, human beings will continue to live on this blue planet named Earth. Our planet has limited space, resources and environmental carrying capacity, yet the human population and quality of life will continue to rise. Economic development and environmental protection are often conflicting goals, and it is a great challenge for us to achieve both at the same time: to develop sustainably. Green chemistry—the aim of making the whole industrial chain of chemistry and chemical industry environmentally friendly—has contributed, and will further contribute, to the sustainable development of the chemical industry. Recently, NSR talked with Buxing Han—an academician of the Chinese Academy of Sciences and one of the leading scientists in this field. Han introduced the major scientific issues of green chemistry and talked about the challenges and future developments of this field.

The porous TiO2 nanotubes/Ag3PO4 heterojunction are synthesized via simple electrospining and chemical co-deposition method. The results of SEM, XRD, TEM and XPS imply that the Ag3PO4 nanoparticles have been introduced on to the surface of TiO2 nanotubes successfully. Compared with the unmodified samples, the photocatalytic activity of the as-prepared porous TiO2 nanotubes/Ag3PO4 heterojunction exhibit a remarkable enhancement by the degradation of methylene blue (MB) under the sunlight. Further, the Z-Scheme structure of the samples and the porous-tubular structure of the TiO2 are considered as the main reasons for the enhancement.

The dual function carbon quantum dots (C QDs) modified porous g-C3N4/TiO2 two dimension (2D) nano-heterojunctions are prepared by a simple route, through which the porous g-C3N4 nanosheets are prepared by thermal polycondensation, the TiO2 nanoparticles are introduced by hydrothermal method and the C QDs are introduced on the surface of the porous g-C3N4 and TiO2 by coupling successively. The results indicate that TiO2 and C QDs are well combined with the porous g-C3N4. The hydrogen production properties of those 2D nano-heterojunctions are investigated, which exhibit an obvious hydrogen production enhancement (nearly two orders of magnitude) compared with those of the unmodified samples. Through analysis, this enhancement of the photocatalystic hydrogen production is attributed to the dual function C QDs with high catalytic activity of H2O2 decomposition and unique up-conversion photoluminescence.

Smart phones, video, computer games, social platforms and mobile payments have dramatically changed our daily lives in the past 10 years. Behind the rise of the internet industry, fourth-generation (4G) network technology played an instrumental role. According to the plans of major communications companies and the global standardization organization 3GPP (3rd Generation Partnership Project), the next generation of wireless network technology (5G) will start to be commercially used before 2020. What will be the technological improvements in performance of 5G comparing with 4G? Would 5G be similarly transformative? In a recent interview with NSR, Huawei's Chief 5G scientist, Wen Tong, talked about these topics, as well as about the transformation of China's communications industry from a technology follower in the eras of 3G and 4G to one of the leading forces behind 5G.

Doping of traditional semiconductors has enabled technological applications in modern electronics by tailoring their chemical, optical and electronic properties. However, substitutional doping in two-dimensional semiconductors is at a comparatively early stage, and the resultant effects are less explored. In this work, we report unusual effects of degenerate doping with Nb on structural, electronic and optical characteristics of MoS2 crystals. The doping readily induces a structural transformation from naturally occurring 2H stacking to 3R stacking. Electronically, a strong interaction of the Nb impurity states with the host valence bands drastically and nonlinearly modifies the electronic band structure with the valence band maximum of multilayer MoS2 at the Γ point pushed upward by hybridization with the Nb states. When thinned down to monolayers, in stark contrast, such significant nonlinear effect vanishes, instead resulting in strong and broadband photoluminescence via the formation of exciton complexes tightly bound to neutral acceptors.

The OER process would be a mainly factor for restricting overall water splitting, so the matching of HER/OER would be an important issue. Herein, the MnOx/CdS/Ti3+-SrTiO3 core–shell heterojunction is fabricated via a continuous hydrothermal-annealing-chemical-photodeposition method. Evaluated by the photocatalytic performance, the MnOx/CdS/Ti3+-SrTiO3 exhibits an enhanced HER performance of about ~ 10 folds than that of pure SrTiO3 nanosphere, and achieves a decent overall water splitting performance of about ~ 176.07(H2)/86.03(O2) μmol/g∙h, which can be mainly ascribed to the well matched HER/OER process and formation of heterojunction. There, the new potential induced by Ti3+/Ov can increase the solar efficiency and accelerate the photo-generated electrons diffusion, the Ti3+ ions can reduced water splitting activation barrier to enhance the H+ reduction, the MnOx with mixed chemical valance Mn3+/Mn4+ ions can activate the hole­related species and promote the H2O2 decomposition, and the core–shell CdS/Ti3+-SrTiO3 heterojunction with appropriate potential gradient can improve the charge carrier separation and transport. Additionally, the core–shell structure can inhibit the photocorrosion to maintain good photocatalytic stability.

The dynamic simulation of the continuous catalytic reforming process is of great significance to the performance prediction and optimization of the entire process. In this study, a 34-lumped mechanism model described by differential algebra was established based on the actual process conditions of the continuous catalytic reforming process in China, and an efficient dynamic simulation solution method based on simultaneous equations was proposed. First, a 34-lumped differential–algebraic mechanism model was established based on the basic principles of reforming kinetics, thermodynamics, material balance, and energy balance. Secondly, in order to solve and simulate the mechanism model composed of 144 differential equations and several algebraic equations, the method of finite-element collocation is used to discretize the differential equations and convert them into large-scale, nonlinear programming problems, and the interior point algorithm is used to estimate its parameters and verify the model. In addition, in order to avoid the problem of too long derivative solution time and too large memory in the solution process, methods such as sparse derivative and Broyden–Fletcher–Goldfarb–Shanno (BFGS) with limited storage are used to solve the problem. Finally, on the basis of model verification, dynamic simulation and sensitivity analysis of the whole process are carried out by modifying different input parameters. The results show that the mechanism model and solution method presented in this paper can quickly and accurately simulate the continuous catalytic reforming process dynamically.

Video game streaming (VGS) has attracted hundreds of millions of viewers all over the world to not only watch but also participate in a variety of VGS activities, such as interacting with streamers and other co-viewers, gift-giving, and social sharing of the viewing experience. The success of the VGS paradigm depends on the active participation of the viewers, since it creates economic, hedonic, and social values. This study applied a mixed-methods approach to explore the critical environmental stimuli evoking viewers’ cognitive and emotional state and empirically tested a research model examining viewers’ participation. Using qualitative interviews, three environmental stimuli were identified (i.e., broadcaster appeal, medium appeal, and perceived co-viewer involvement), which were adopted in the quantitative research model. The research findings suggested that environmental stimuli were positively related to both cognitive and emotional organisms, namely cognitive involvement and arousal, which in turn impacted viewers’ participation.

The Z-Scheme Ag3PO4/Ag/g-C3N4 nanosheets composites are synthesised via simple annealing and anion-exchange precipitation method. The obtained samples are characterized by SEM, XRD, TEM, XPS, UV–Vis and PL, which imply that the Z-Scheme Ag3PO4/Ag/g-C3N4 structure has been prepared successfully. The photocatalytic activity of the as-prepared Ag3PO4/Ag/g-C3N4 nanosheets composites displays a remarkable enhancement after the Ag3PO4/Ag nanoparticles being introduced by the hydrogen production under visible light. Further, the Z-Scheme structure of the sample and the lamellar structure of the C3N4 are considered as the main reasons for the enhancement.

Scientists have been aware of the phenomenon of superwettability for more than two centuries. In 1805, British scientist Thomas Young introduced the concept of the contact angle to evaluate the wettability of liquid on a solid material surface. Superwettable materials have only become a fast-developing research area over the past two decades, with scientists beginning to investigate and mimic the micro-/nanostructures of natural superwettable materials. Elucidation of the micro-/nanostructures of natural superwettable materials, from superhydrophobic lotus leaves and superhydrophilic spider silk to superoleophobic (oil-repelling) fish scales, has greatly propelled the development of this field. Superwettable materials have found wide applications such as liquid–liquid separation, sensors and energy conversion devices. Lei Jiang, an academician of the Chinese Academy of Sciences, a fellow of The World Academy of Sciences (TWAS) and a foreign member of the US National Academy of Engineering, is a pioneer in the field of bio-inspired superwettable materials. He proposed the ‘binary cooperative complementary principle’ that nanoscale structural arrangements of two materials with complementary properties can result in functional macroscopic materials, which provided a framework for the design of superwettable materials. In this recent NSR interview, Jiang discussed the theory and applications of this field over the past two decades, and reflected upon innovative scientific research in general.

We report on efficient carrier-to-exciton conversion and planar electroluminescence from tunnel diodes based on a metal–insulator–semiconductor (MIS) van der Waals heterostack consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer tungsten disulfide (WS2). These devices exhibit excitonic electroluminescence with extremely low threshold current density of a few pA·μm–2, which is several orders of magnitude lower compared to the previously reported values for the best planar EL devices. Using a reference dye, we estimate the EL quantum efficiency to be ∼1% at low current density limit, which is of the same order of magnitude as photoluminescence quantum yield at the equivalent excitation rate. Our observations reveal that the efficiency of our devices is not limited by carrier-to-exciton conversion efficiency but by the inherent exciton-to-photon yield of the material. The device characteristics indicate that the light emission is triggered by injection of hot minority carriers...

‘Blinking’, or ‘fluorescence intermittency’, refers to a random switching between ‘ON’ (bright) and ‘OFF’ (dark) states of an emitter; it has been studied widely in zero-dimensional quantum dots1 and molecules2, 3, and scarcely in one-dimensional systems4, 5. A generally accepted mechanism for blinking in quantum dots involves random switching between neutral and charged states6, 7 (or is accompanied by fluctuations in charge-carrier traps8), which substantially alters the dynamics of radiative and non-radiative decay. Here, we uncover a new type of blinking effect in vertically stacked, two-dimensional semiconductor heterostructures9, which consist of two distinct monolayers of transition metal dichalcogenides (TMDs) that are weakly coupled by van der Waals forces. Unlike zero-dimensional or one-dimensional systems, two-dimensional TMD heterostructures show a correlated blinking effect, comprising randomly switching bright, neutral and dark states. Fluorescence cross-correlation spectroscopy analyses show that a bright state occurring in one monolayer will simultaneously lead to a dark state in the other monolayer, owing to an intermittent interlayer carrier-transfer process. Our findings suggest that bilayer van der Waals heterostructures provide unique platforms for the study of charge-transfer dynamics and non-equilibrium-state physics, and could see application as correlated light emitters in quantum technology. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore)

As one of the major search engines in the world, Baidu's Sponsored Search has long adopted the use of deep neural network (DNN) models for Ads click-through rate (CTR) predictions, as early as in 2013. The input futures used by Baidu's online advertising system (a.k.a. "Phoenix Nest'') are extremely high-dimensional (e.g., hundreds or even thousands of billions of features) and also extremely sparse. The size of the CTR models used by Baidu's production system can well exceed 10TB. This imposes tremendous challenges for training, updating, and using such models in production. For Baidu's Ads system, it is obviously important to keep the model training process highly efficient so that engineers (and researchers) are able to quickly refine and test their new models or new features. Moreover, as billions of user ads click history entries are arriving every day, the models have to be re-trained rapidly because CTR prediction is an extremely time-sensitive task. Baidu's current CTR models are trained on MPI (Message Passing Interface) clusters, which require high fault tolerance and synchronization that incur expensive communication and computation costs. And, of course, the maintenance costs for clusters are also substantial. This paper presents AIBox, a centralized system to train CTR models with tens-of-terabytes-scale parameters by employing solid-state drives (SSDs) and GPUs. Due to the memory limitation on GPUs, we carefully partition the CTR model into two parts: one is suitable for CPUs and another for GPUs. We further introduce a bi-level cache management system over SSDs to store the 10TB parameters while providing low-latency accesses. Extensive experiments on production data reveal the effectiveness of the new system. AIBox has comparable training performance with a large MPI cluster, while requiring only a small fraction of the cost for the cluster.

Hepatology and drug development for liver diseases require in vitro liver models. Typical models include 2D planar primary hepatocytes, hepatocyte spheroids, hepatocyte organoids, and liver-on-a-chip. Liver-on-a-chip has emerged as the mainstream model for drug development because it recapitulates the liver microenvironment and has good assay robustness such as reproducibility. Liver-on-a-chip with human primary cells can potentially correlate clinical testing. Liver-on-a-chip can not only predict drug hepatotoxicity and drug metabolism, but also connect other artificial organs on the chip for a human-on-a-chip, which can reflect the overall effect of a drug. Engineering an effective liver-on-a-chip device requires knowledge of multiple disciplines including chemistry, fluidic mechanics, cell biology, electrics, and optics. This review first introduces the physiological microenvironments in the liver, especially the cell composition and its specialized roles, and then summarizes the strategies to build a liver-on-a-chip via microfluidic technologies and its biomedical applications. In addition, the latest advancements of liver-on-a-chip technologies are discussed, which serve as a basis for further liver-on-a-chip research.

Non-parenchymal cells play a key role in the occurrence and development of alcoholic liver disease. However, this cellular behaviour has not been fully characterized, and it is inconvenient to observe in traditional in vitro alcoholic liver disease (ALD) models and animal models. Herein we developed a demountable liver-on-chip device for investigation of pathophysiological process of individual non-parenchymal cells in alcohol induced ALD. This liver-device comprised of HepG2, LX-2, EAhy926 and U937 cells, which were ordered in a physiological distribution under perfuse. This device allows improved HepG2 cells activities and maintained high liver functions which including albumin synthesis and urea secretion. This novel liver-device is able to recreate the damage process of hepatic non-parenchymal cell lines induced by alcohol, and to understand the intercellular communication between different types of hepatic cells during ALD by measuring multiple biomarkers of each types of hepatic non-parenchymal cell lines, including Ve-cadherin, eNOS, VEGF and α-SMA. The proposed liver-device is able to further studies of pathological analysis and drug- and toxicity-screening.

The poor metabolic ability of cell lines fails to meet the requirements of an in vitro model for drug interaction testing which is crucial for the development or clinical application of drugs. Herein, we describe a liver sinusoid-on-a-chip device composed of four kinds of transformed cell lines (HepG2 cells, LX-2 cells, EAhy926 cells, and U937 cells) that were ordered in a physiological distribution with artificial liver blood flow and biliary efflux flowing in the opposite direction. This microfluidic device applied three-dimensional culturing of HepG2 cells with high density (10(7) ml(−1)), forming a tightly connected monolayer of EAhy926 cells and achieving the active transport of drugs in HepG2 cells. Results showed that the device maintained synthetic and secretory functions, preserved cytochrome P450 1A1/2 and uridine diphosphate glucuronyltransferase enzymatic activities, as well as sensitivity of drug metabolism. The cell lines derived device enables the investigation of a drug-drug interaction study. We used it to test the hepatotoxicity of acetaminophen and the following combinations: “acetaminophen + rifampicin,” “acetaminophen + omeprazole,” and “acetaminophen + ciprofloxacin.” The variations in hepatotoxicity of the combinations compared to acetaminophen alone, which is not found in a 96-well plate model, in the device were −17.15%, 14.88%, and −19.74%. In addition, this result was similar to the one tested by the classical primary hepatocyte plate model (−13.22%, 13.51%, and −15.81%). Thus, this cell lines derived liver model provides an alternative to investigate drug hepatotoxicity, drug-drug interaction.

Impressive properties arise from the atomically thin nature of transition metal dichalcogenide two-dimensional materials. However, being atomically thin limits their optical absorption or emission. Hence, enhancing their photoluminescence by plasmonic nanostructures is critical for integrating these materials in optoelectronic and photonic devices. Typical photoluminescence enhancement from transition metal dichalcogenides is 100-fold, with recent enhancement of 1,000-fold achieved by simultaneously enhancing absorption, emission and directionality of the system. By suspending WSe2 flakes onto sub-20-nm-wide trenches in gold substrate, we report a giant photoluminescence enhancement of ∼20,000-fold. It is attributed to an enhanced absorption of the pump laser due to the lateral gap plasmons confined in the trenches and the enhanced Purcell factor by the plasmonic nanostructure. This work demonstrates the feasibility of giant photoluminescence enhancement in WSe2 with judiciously designed plasmonic nanostructures and paves a way towards the implementation of plasmon-enhanced transition metal dichalcogenide photodetectors, sensors and emitters., Two-dimensional materials have excellent electrical properties, but poor luminescence limits their application in optoelectronics. Here, the authors demonstrate a plasmon-induced 20,000-fold enhancement in photoluminescence from tungsten diselenide suspended across a nanometre-scale gap.

Carcinoembryonic antigen (CEA) is a wide-spectrum biomarker. Clinically, we generally use serum sample to detect CEA, which needs to be centrifuged to pretreat the raw blood sample. In this study, we realized direct CEA detection in raw blood samples exploiting microfluidics. The LOD was as low as 10(-12) M.

The Ag-K2Nb2O6 nanocomposites are synthesized by a two-step method where the octahedral K2Nb2O6 is initially prepared by solvothermal reaction and then the Ag particles are anchored onto the surface of K2Nb2O6 through the photoreduction of AgNO3. The XRD, SEM, TEM, XPS, DRS are applied to characterize the structure, morphology and optical properties, which confirm that the Ag particles are successfully deposited on the surface of K2Nb2O6. Compared with the pure K2Nb2O6, the Ag modified K2Nb2O6 catalysts show an obvious enhancement catalysis under UV–Vis light, because that could efficiently promote the light absorption and the separation of photoelectrons and holes.

This study presented a composite biomaterial ink consisting of GelMA, decellularized extracellular matrix (DECM) and nanoclay for printing 3D scaffolds for primary hepatocytes cultivation. In this biomaterial ink, the proportion of DECM was 75%, which is the highest value ever reported. The high proportion of DECM resulted in high activity of primary hepatocytes, and enabled better organ-specific biomaterial ink.

The flexible-transparent N-doped Cu2O/SnO2 p-n junction film device is prepared via a simple hybrid hydrothermal-sputtering method. There, the SnO2 nanowire arrays are induced by the pre-sputtered seeds and grown on the flexible PEN substrate via hydrothermal method, and subsequently the N-doped Cu2O film is deposited via radio-frequency sputtering. As revealed, the flexible-transparent device exhibits highly transmittance of about ~85% in visible light, obvious photovoltaic conversion enhancement of about ~1500 folds than the undoped device, and decent flexible stability of about ~91% during the 1000 times bending, which is regarded as a decent flexible-transparent photovoltaic device and can be mainly ascribed to the N-doping can regulate the band gap to increase the transmittance, reduce the crystal defect to improve the charge carriers, including the interface transport rate and lifetime, the orderly SnO2 nano-arrays can release the interfacial stress to increase the flexible stability.

Long-range coherent polariton condensate flow is observed in all-inorganic perovskite microcavities., Novel technological applications significantly favor alternatives to electrons toward constructing low power–consuming, high-speed all-optical integrated optoelectronic devices. Polariton condensates, exhibiting high-speed coherent propagation and spin-based behavior, attract considerable interest for implementing the basic elements of integrated optoelectronic devices: switching, transport, and logic. However, the implementation of this coherent polariton condensate flow is typically limited to cryogenic temperatures, constrained by small exciton binding energy in most semiconductor microcavities. Here, we demonstrate the capability of long-range nonresonantly excited polariton condensate flow at room temperature in a one-dimensional all-inorganic cesium lead bromide (CsPbBr3) perovskite microwire microcavity. The polariton condensate exhibits high-speed propagation over macroscopic distances of 60 μm while still preserving the long-range off-diagonal order. Our findings pave the way for using coherent polariton condensate flow for all-optical integrated logic circuits and polaritonic devices operating at room temperature.

The 2D(two-dimension) nickel‑molybdenum bimetals sulfide synergistic modified hollow cubic CdS is fabricated by the continuous chemical precipitation, vulcanized and hydrothermal methods, there, the hollow cubic CdS is vulcanized from the CdCO3 and then the 2D Ni-Mo-S lamellas grow on the surface of the CdS. Evaluated by the photocatalytic hydrogen production, the photocatalytic performance of the CdS/Ni-Mo-S exhibits an obvious enhancement of about ~80 folds than the single CdS. Studied by the electrochemical measurements, the main reasons for the HER(hydrogen evolution reaction) enhancement are ascribed to that the Pt-like behavior bimetals Ni-Mo-S can quickly accept and transfer-diffuse the photo-generated electrons to water, the 2D ultrathin lamellas can provide sufficient HER active sites and shorten the transferring time, and the hollow nanostructure can increase the solar utilization.

As applications continue to generate multi-dimensional data at exponentially increasing rates, fast analytics to extract meaningful results is becoming extremely important. The database community has developed array databases that alleviate this problem through a series of techniques. In-situ mechanisms provide direct access to raw data in the original format---without loading and partitioning. Parallel processing scales to the largest datasets. In-memory caching reduces latency when the same data are accessed across a workload of queries. However, we are not aware of any work on distributed caching of multi-dimensional raw arrays. In this paper, we introduce a distributed framework for cost-based caching of multi-dimensional arrays in native format. Given a set of files that contain portions of an array and an online query workload, the framework computes an effective caching plan in two stages. First, the plan identifies the cells to be cached locally from each of the input files by continuously refining an evolving R-tree index. In the second stage, an optimal assignment of cells to nodes that collocates dependent cells in order to minimize the overall data transfer is determined. We design cache eviction and placement heuristic algorithms that consider the historical query workload. A thorough experimental evaluation over two real datasets in three file formats confirms the superiority - by as much as two orders of magnitude - of the proposed framework over existing techniques in terms of cache overhead and workload execution time.

Methods for making interfaces between atomically thin sheets of materials might open the way to a range of nanotechnologies. A practically simple method has been reported, based on the cyclical switching of gaseous reagents. Methods for making interfaces between atomically thin sheets of materials might open the way to a range of nanotechnologies. A practically simple method has been reported, based on the cyclical switching of gaseous reagents.

© 2018 Inderscience Enterprises Ltd. Palomar Transient Factory (PTF) is a comprehensive detection system for the identification and classification of transient astrophysical objects. In this paper, we make two significant contributions to the PTF pipeline. First, we present an experimental study that evaluates a novel implementation of the real-time classifier in GLADE - a parallel data processing system that combines the efficiency of a database with the extensibility of map-reduce. We show how each stage in the classifier maps optimally into GLADE tasks by taking advantage of the unique features of the system - range-based data partitioning, columnar storage, multi-query execution, and in-database support for complex aggregate computation. Second, we introduce a novel parallel similarity join algorithm for advanced transient classification. We implement this algorithm in GLADE and execute it on a massive supercomputer with more than 3,000 threads, achieving more than three orders of magnitude improvement over the PostgreSQL solution.

Chemical vapor deposition (CVD) of two-dimensional (2D) materials such as monolayer MoS2 typically involves the conversion of vapor-phase precursors to a solid product in a process that may be described as a vapor-solid-solid (VSS) mode. Here, we report the first demonstration of vapor-liquid-solid (VLS) growth of monolayer MoS2 yielding highly crystalline ribbon-shaped structures with a width of a few tens of nanometers to a few micrometers. The VLS growth mode is triggered by the reaction between molybdenum oxide and sodium chloride, which results in the formation of molten Na-Mo-O droplets. These droplets mediate the growth of MoS2 ribbons in the "crawling mode" when saturated with sulfur on a crystalline substrate. Our growth yields straight and kinked ribbons with a locally well-defined orientation, reflecting the regular horizontal motion of the liquid droplets during growth. Using atomic-resolution scanning transmission electron microscopy (STEM) and second harmonic generation (SHG) microscopy, we show that the ribbons are homoepitaxially on monolayer MoS2 surface with predominantly 2H- or 3R-type stacking. These findings pave the way to novel devices with structures of mixed dimensionalities., Comment: 40 pages, 19 figures

Modulating second harmonic generation (SHG) by a static electric field through either electric-field-induced SHG or charge-induced SHG has been well documented. Nonetheless, it is essential to develop the ability to dynamically control and manipulate the nonlinear properties, preferably at high speed. Plasmonic hot carriers can be resonantly excited in metal nanoparticles and then injected into semiconductors within 10–100 fs, where they eventually decay on a comparable time scale. This allows one to rapidly manipulate all kinds of characteristics of semiconductors, including their nonlinear properties. Here we demonstrate that plasmonically generated hot electrons can be injected from plasmonic nanostructure into bilayer (2L) tungsten diselenide (WSe2), breaking the material inversion symmetry and thus inducing an SHG. With a set of pump–probe experiments we confirm that it is the dynamic separation electric field resulting from the hot carrier injection (rather than a simple optical field enhancement) that is the cause of SHG. Transient absorption measurement further substantiate the plasmonic hot electrons injection and allow us to measure a rise time of ∼120 fs and a fall time of 1.9 ps. Our study creates opportunity for the ultrafast all-optical control of SHG in an all-optical manner that may enable a variety of applications. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version