Two-dimensional (2D) materials have been studied extensively as monolayers, vertical or lateral heterostructures. To achieve functionalization, monolayers are often patterned using soft lithography ...and selectively decorated with molecules. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe
can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.
A Nationwide Nitrogen Deposition Monitoring Network (NNDMN) containing 43 monitoring sites was established in China to measure gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3− in air and/or ...precipitation from 2010 to 2014. Wet/bulk deposition fluxes of Nr species were collected by precipitation gauge method and measured by continuous-flow analyzer; dry deposition fluxes were estimated using airborne concentration measurements and inferential models. Our observations reveal large spatial variations of atmospheric Nr concentrations and dry and wet/bulk Nr deposition. On a national basis, the annual average concentrations (1.3–47.0 μg N m−3) and dry plus wet/bulk deposition fluxes (2.9–83.3 kg N ha−1 yr−1) of inorganic Nr species are ranked by land use as urban > rural > background sites and by regions as north China > southeast China > southwest China > northeast China > northwest China > Tibetan Plateau, reflecting the impact of anthropogenic Nr emission. Average dry and wet/bulk N deposition fluxes were 20.6 ± 11.2 (mean ± standard deviation) and 19.3 ± 9.2 kg N ha−1 yr−1 across China, with reduced N deposition dominating both dry and wet/bulk deposition. Our results suggest atmospheric dry N deposition is equally important to wet/bulk N deposition at the national scale. Therefore, both deposition forms should be included when considering the impacts of N deposition on environment and ecosystem health.
Universal quantum computation1 is striking for its unprecedented capability in processing information, but its scalability is challenging in practice because of the inevitable environment noise. ...Although quantum error correction (QEC) techniques2–8 have been developed to protect stored quantum information from leading orders of error, the noise-resilient processing of the QEC-protected quantum information is highly demanded but remains elusive9. Here, we demonstrate phase gate operations on a logical qubit encoded in a bosonic oscillator in an error-transparent (ET) manner. Inspired by refs. 10,11, the ET gates are extended to the bosonic code and are able to tolerate errors on the logical qubit during gate operations, regardless of the random occurrence time of the error. With precisely designed gate Hamiltonians through photon-number-resolved a.c. Stark shifts, the ET condition is fulfilled experimentally. We verify that the ET gates outperform the non-ET gates with a substantial improvement of gate fidelity after an occurrence of the single-photon-loss error. Our ET gates in superconducting quantum circuits can be readily extended to multiple encoded qubits and a universal gate set is within reach, holding the potential for reliable quantum information processing.Error-transparent quantum gates that can tolerate certain error during the execution of quantum operations have been demonstrated. Substantial improvement of the gate fidelity sheds lights on large-scale universal quantum computation.
Machine learning, a branch of artificial intelligence, learns from previous experience to optimize performance, which is ubiquitous in various fields such as computer sciences, financial analysis, ...robotics, and bioinformatics. A challenge is that machine learning with the rapidly growing "big data" could become intractable for classical computers. Recently, quantum machine learning algorithms Lloyd, Mohseni, and Rebentrost, arXiv.1307.0411 were proposed which could offer an exponential speedup over classical algorithms. Here, we report the first experimental entanglement-based classification of two-, four-, and eight-dimensional vectors to different clusters using a small-scale photonic quantum computer, which are then used to implement supervised and unsupervised machine learning. The results demonstrate the working principle of using quantum computers to manipulate and classify high-dimensional vectors, the core mathematical routine in machine learning. The method can, in principle, be scaled to larger numbers of qubits, and may provide a new route to accelerate machine learning.
Cloud top and tropopause relationships are examined using cloud top observations from the Cloud‐Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) cloud data and National Centers for ...Environmental Prediction Global Forecast System (GFS) tropopause data. Statistical analyses of cloud top occurrence in tropopause and jet referenced relative altitude coordinates are performed on a global scale using 4 years (2006–2010) of CALIPSO 5 km resolution cloud layer data. The results show that the thermal tropopause appears to be a significant constraint for the cloud top. The zonal vertical distribution of cloud tops in tropopause‐relative coordinates shows a maximum at the tropopause level for both the tropics (20°S–20°N) and midlatitudes (40°–60°S, 40°–60°N) for all four seasons. Occurrence of cloud tops above the tropopause is examined and quantified. The results show that with the consideration of tropopause height uncertainty, the data do not provide sufficient evidence of significant presence of cloud tops above the tropopause in the midlatitudes. In the tropics, the significant occurrences of cloud top above the thermal tropopause are found in regions known for seasonal deep convection. In most cases, the occurrence is up to 24% in 2° × 3° latitude‐longitude bins with isolated higher frequencies in the western Pacific during the northern hemispheric winter season. The vertical distributions show that these events are mostly up to 2.5 km above the lapse rate tropopause, which is comparable to the differences between the lapse rate and the cold point tropopause in regions of active convection. We speculate that this separation may be responsible for a significant fraction of the cloud tops that do occur above the lapse rate tropopause in our analyses. It is also important to note that our results are limited by the CALIPSO twice‐daily sampling with local equator crossing times of 0130 and 1330. The data therefore do not provide a good representation of convection over land, which is known to have maxima in afternoon local times. The tropopause determination is a significant component of this type of studies, and errors in the tropopause height may lead to significantly different conclusions. Our analyses show that the tropopause product from the GFS model is in better agreement with radiosonde measurements. The Goddard Earth Observing System Model Version 5 tropopause product, given as the ancillary data in the CALIPSO data file, shows a much larger uncertainty, primarily because the tropopause is identified at the model grid levels.
Key Points
The tropopause is a significant boundary for the cloud tops
No sufficient evidence of cloud tops above the tropopause in the midlatitudes
Occurrences of cloud top above the LRT may be in part due to LRT/CPT differences
Hypoxia plays a critical role during the evolution of malignant cells and tumour microenvironment (TME).Tumour-derived exosomes contain informative microRNAs involved in the interaction of cancer and ...stromal cells, thus contributing to tissue remodelling of tumour microenvironment. This study aims to clarify how hypoxia affects tumour angiogenesis through exosomes shed from lung cancer cells. Lung cancer cells produce more exosomes under hypoxic conditions than do parental cells under normoxic conditions. miR-23a was significantly upregulated in exosomes from lung cancer under hypoxic conditions. Exosomal miR-23a directly suppressed its target prolyl hydroxylase 1 and 2 (PHD1 and 2), leading to the accumulation of hypoxia-inducible factor-1 α (HIF-1 α) in endothelial cells. Consequently, hypoxic lung cancer cells enhanced angiogenesis by exosomes derived from hypoxic cancer under both normoxic and hypoxic conditions. In addition, exosomal miR-23a also inhibits tight junction protein ZO-1, thereby increasing vascular permeability and cancer transendothelial migration. Inhibition of miR-23a by inhibitor administration decreased angiogenesis and tumour growth in a mouse model. Furthermore, elevated levels of circulating miR-23a are found in the sera of lung cancer patients, and miR-23a levels are positively correlated with proangiogenic activities. Taken together, our study reveals the clinical relevance and prognostic value of cancer-derived exosomal miR-23a under hypoxic conditions, and investigates a unique intercellular communication, mediated by cancer-derived exosomes, which modulates tumour vasculature.
The Model for Ozone and Related Chemical Tracers, version 3 (MOZART‐3), which represents the chemical and physical processes from the troposphere through the lower mesosphere, was used to evaluate ...the representation of long‐lived tracers and ozone using three different meteorological fields. The meteorological fields are based on (1) the Whole Atmosphere Community Climate Model, version 1b (WACCM1b), (2) the European Centre for Medium‐Range Weather Forecasts (ECMWF) operational analysis, and (3) a new reanalysis for year 2000 from ECMWF called EXP471. Model‐derived tracers (methane, water vapor, and total inorganic nitrogen) and ozone are compared to data climatologies from satellites. Model mean age of air was also derived and compared to in situ CO2 and SF6 data. A detailed analysis of the chemical fields simulated by MOZART‐3 shows that even though the general features characterizing the three dynamical sets are rather similar, slight differences in winds and temperature can produce substantial differences in the calculated distributions of chemical tracers. The MOZART‐3 simulations that use meteorological fields from WACCM1b and ECMWF EXP471 represented best the distribution of long‐lived tracers and mean age of air in the stratosphere. There was a significant improvement using the ECMWF EXP471 reanalysis data product over the ECMWF operational data product. The effect of the quasi‐biennial oscillation circulation on long‐lived tracers and ozone is examined.
ABSTRACT
Scaling laws of dust, H i gas, and metal mass with stellar mass, specific star formation rate, and metallicity are crucial to our understanding of the build-up of galaxies through their ...enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass (MH i/M⋆) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) – including stellar dust production, grain growth, and dust destruction – within a Bayesian framework to enable a rigorous search of the multidimensional parameter space. We find that these scaling laws for galaxies with −1.0 ≲ log MH i/M⋆ ≲ 0 can be reproduced using closed-box models with high fractions (37–89 ${{\ \rm per\ cent}}$) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies (ϵ = 30–40), and long dust lifetimes (1–2 Gyr). The models have present-day dust masses with similar contributions from stellar sources (50–80 ${{\ \rm per\ cent}}$) and grain growth (20–50 ${{\ \rm per\ cent}}$). Over the entire lifetime of these galaxies, the contribution from stardust (>90 ${{\ \rm per\ cent}}$) outweighs the fraction of dust grown in the interstellar medium (<10 ${{\ \rm per\ cent}}$). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth time-scales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium.
Abstract
Topological superconductors (TSCs) are unconventional superconductors with bulk superconducting gap and in-gap Majorana states on the boundary that may be used as topological qubits for ...quantum computation. Despite their importance in both fundamental research and applications, natural TSCs are very rare. Here, combining state of the art synchrotron and laser-based angle-resolved photoemission spectroscopy, we investigated a stoichiometric transition metal dichalcogenide (TMD), 2M-WS
2
with a superconducting transition temperature of 8.8 K (the highest among all TMDs in the natural form up to date) and observed distinctive topological surface states (TSSs). Furthermore, in the superconducting state, we found that the TSSs acquired a nodeless superconducting gap with similar magnitude as that of the bulk states. These discoveries not only evidence 2M-WS
2
as an intrinsic TSC without the need of sensitive composition tuning or sophisticated heterostructures fabrication, but also provide an ideal platform for device applications thanks to its van der Waals layered structure.
Human activities, especially conversion and degradation of habitats, are causing global biodiversity declines. How local ecological assemblages are responding is less clear--a concern given their ...importance for many ecosystem functions and services. We analysed a terrestrial assemblage database of unprecedented geographic and taxonomic coverage to quantify local biodiversity responses to land use and related changes. Here we show that in the worst-affected habitats, these pressures reduce within-sample species richness by an average of 76.5%, total abundance by 39.5% and rarefaction-based richness by 40.3%. We estimate that, globally, these pressures have already slightly reduced average within-sample richness (by 13.6%), total abundance (10.7%) and rarefaction-based richness (8.1%), with changes showing marked spatial variation. Rapid further losses are predicted under a business-as-usual land-use scenario; within-sample richness is projected to fall by a further 3.4% globally by 2100, with losses concentrated in biodiverse but economically poor countries. Strong mitigation can deliver much more positive biodiversity changes (up to a 1.9% average increase) that are less strongly related to countries' socioeconomic status.
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