Adversarial Sparse-View CBCT Artifact Reduction

We present an effective post-processing method to reduce the artifacts from sparsely reconstructed cone-beam CT (CBCT) images. The proposed method is based on the state-of-the-art, image-to-image generative models with a perceptual loss as regulation. Unlike the traditional CT artifact-reduction approaches, our method is trained in an adversarial fashion that yields more perceptually realistic outputs while preserving the anatomical structures. To address the streak artifacts that are inherently local and appear across various scales, we further propose a novel discriminator architecture based on feature pyramid networks and a differentially modulated focus map to induce the adversarial training. Our experimental results show that the proposed method can greatly correct the cone-beam artifacts from clinical CBCT images reconstructed using 1/3 projections, and outperforms strong baseline methods both quantitatively and qualitatively

Retrieval of phase memory in two independent atomic ensembles by Raman process

In spontaneous Raman process in atomic cell at high gain, both the Stokes field and the accompanying collective atomic excitation (atomic spin wave) are coherent. We find that, due to the spontaneous nature of the process, the phases of the Stokes field and the atomic spin wave change randomly from one realization to another but are anti-correlated. The phases of the atomic ensembles are read out via another Raman process at a later time, thus realizing phase memory in atoms. The observation of phase correlation between the Stokes field and the collective atomic excitations is an important step towards macroscopic EPR-type entanglement of continuous variables between light and atoms

Benchmarking explanatory models for inertia forecasting using public data of the nordic area

This paper investigates the performance of a day-ahead explanatory model for inertia forecasting based on field data in the Nordic system, which achieves a 43% reduction in mean absolute percentage error (MAPE) against a state-of-the-art time-series forecast model. The generalizability of the explanatory model is verified by its consistent performance on Nordic and Great Britain datasets. Also, it appears that a long duration of training data is not required to obtain accurate results with this model, but taking a more spatially granular approach reduces the MAPE by 3.6%. Finally, two further model enhancements are studied considering the specific features in Nordic system: (i) a monthly interaction variable applied to the day-ahead national demand forecast feature, reducing the MAPE by up to 18%; and (ii) a feature based on the inertia from hydropower, although this has a negligible impact. The field dataset used for benchmarking is also made publicly available

A novel method for deriving the aerosol hygroscopicity parameter based only on measurements from a humidified nephelometer system

Aerosol hygroscopicity is crucial for understanding roles of aerosol particles in atmospheric chemistry and aerosol climate effects. Light-scattering enhancement factor f(RH, λ) is one of the parameters describing aerosol hygroscopicity, which is defined as f(RH, λ) = σsp(RH, λ)∕σsp(dry, λ), where σsp(RH, λ) or σsp(dry, λ) represents σsp at wavelength λ under certain relative humidity (RH) or dry conditions. Traditionally, an overall hygroscopicity parameter κ can be retrieved from measured f(RH, λ), hereinafter referred to as κf(RH), by combining concurrently measured particle number size distribution (PNSD) and mass concentration of black carbon. In this paper, a new method is proposed to directly derive κf(RH) based only on measurements from a three-wavelength humidified nephelometer system. The advantage of this newly proposed approach is that κf(RH) can be estimated without any additional information about PNSD and black carbon. This method is verified with measurements from two different field campaigns. Values of κf(RH) estimated from this new method agree very well with those retrieved by using the traditional method: all points lie near the 1 : 1 line and the square of correlation coefficient between them is 0.99. The verification results demonstrate that this newly proposed method of deriving κf(RH) is applicable at different sites and in seasons of the North China Plain and might also be applicable in other regions around the world

Strategies and reaction systems for solar-driven CO2 reduction by water

Solar driven CO2 conversion into high-value-added chemicals and energy-rich fuels is one of the promising strategies to tackle global warming and to address the energy-supply crisis. Even though enormous effort has been devoted to exploring all sorts of homogeneous and heterogeneous photocatalysts, the current efficiency and more importantly selectivity to valuable chemicals are still rather moderate, thus it is desired to develop high-efficiency photocatalytic system toward CO2 reduction with excellent selectivity. In this review, fundamental aspects of photocatalytic CO2 reduction by pure water, the reaction systems and the reliable method for detection of the products are firstly described. Thereafter the recent advances of the main strategy for improving the photocatalytic CO2 reduction from the perspective of promoting the CO2 adsorption and activation, accelerating the kinetics of water oxidation, and modulating charge separation are overviewed. The prospects and challenges on precise designing heterogeneous catalysts for CO2 photoreduction are proposed at the end, indicating the significance for the further development of photocatalytic systems with high CO2 conversion efficiency and product selectivity

A study of aerosol liquid water content based on hygroscopicity measurements at high relative humidity in the North China Plain

Water can be a major component of aerosol particles, also serving as a medium for aqueous-phase reactions. In this study, a novel method is presented to calculate the aerosol liquid water content at high relative humidity based on measurements of aerosol hygroscopic growth factor, particle number size distribution and relative humidity in the Haze in China (HaChi) summer field campaign (July–August 2009) in the North China Plain. The aerosol liquid water content calculated using this method agreed well with that calculated using a thermodynamic equilibrium model (ISORROPIA II) at high relative humidity (>60%) with a correlation coefficient of 0.96. At low relative humidity (<60%), an underestimation was found in the calculated aerosol liquid water content by the thermodynamic equilibrium model. This discrepancy mainly resulted from the ISORROPIA II model, which only considered limited aerosol chemical compositions. The mean and maximum values of aerosol liquid water content during the HaChi campaign reached 1.69 × 10&minus;4 g m−3 and 9.71 × 10&minus;4 g m−3, respectively. A distinct diurnal variation of the aerosol liquid water content was found, with lower values during daytime and higher ones at night. The aerosol liquid water content depended strongly on the relative humidity. The aerosol liquid water content in the accumulation mode dominated the total aerosol liquid water content

Open clusters housing classical Cepheids in Gaia DR3

The latest Gaia Data Release 3 provides an opportunity to expand the census of Galactic open clusters harboring classical Cepheid variables, thereby bolstering the cosmic distance scale. A comprehensive analysis yielded a total of 50 classical Cepheids associated with 45 open clusters, of which 39 open cluster-classical Cepheid pairs are considered probable, with the remaining 11 pairs considered improbable but worth following up. Two previously identified clusters by us possibly host classical Cepheids (OC-0125/V1788 Cyg and OC-0675/OGLE-BLG-CEP-114). In addition, we identify 38 new open cluster candidates within the Galactic disk.Comment: 14 pages, 4 figures, Accepted for publication in A&

A comparison of the local spiral structure from Gaia DR2 and VLBI maser parallaxes

Context. The Gaia mission has released the second data set (Gaia DR2), which contains parallaxes and proper motions for a large number of massive, young stars. Aims. We investigate the spiral structure in the solar neighborhood revealed by Gaia DR2 and compare it with that depicted by VLBI maser parallaxes. Methods. We examined three samples with different constraints on parallax uncertainty and distance errors and stellar spectral types: (1) all OB stars with parallax errors of less than 10%; (2) only O-type stars with 0.1 mas errors imposed and with parallax distance errors of less than 0.2 kpc; and (3) only O-type stars with 0.05 mas errors imposed and with parallax distance errors of less than 0.3 kpc. Results. In spite of the significant distance uncertainties for stars in DR2 beyond 1.4 kpc, the spiral structure in the solar neighborhood demonstrated by Gaia agrees well with that illustrated by VLBI maser results. The O-type stars available from DR2 extend the spiral arm models determined from VLBI maser parallaxes into the fourth Galactic quadrant, and suggest the existence of a new spur between the Local and Sagittarius arms.Comment: 4 pages, 3 figures, 1 table, accepted for publication in A&

Synthesis of Silicate-Bridged Heterojunctional SnO2/BiVO4 Nanoplates as Efficient Photocatalysts to Convert CO2 and Degrade 2,4-Dichlorophenol

Bismuth vanadate (BiVO4) is a promising visible‐light responsive photocatalyst, whose photocatalytic activity can be significantly improved by increasing its surface area and utilizing its high‐energy‐level photogenerated electrons effectively. In this work, 2D BiVO4 nanoplates with large specific surface area are successfully fabricated by hydrothermal conversion with the pre‐prepared BiOCl nanosheets as precursors. To improve the photogenerated charge separation, resulted BiVO4 nanoplates are further coupled with nanocrystalline SnO2 to construct heterojunctions, then silicate bridges are introduced between the interfaces of BiVO4 and SnO2. The amount‐optimized silicate‐bridged SnO2/BiVO4 nanocomposite exhibit exceptional visible‐light photocatalytic activities, by ≈7‐time and 4‐time enhancements for CO2 conversion to CH4 and for 2,4‐dichlorophenol degradation, respectively, compared to bare BiVO4 nanoparticles. The significantly enhanced charge separation is verified by steady‐state and time‐resolved surface photovoltage responses and produced hydroxyl radical amounts. Moreover, it is deduced through designed photo‐electrochemical experiments that the introduced SnO2 acts as a proper‐energy platform capable of accepting the photogenerated electrons of BiVO4 nanoplates, and the constructed silicate bridges further facilitate the electron transfer between BiVO4 and SnO2. This work opens up a feasible route to synthesize visible‐light‐driven 2D bismuth‐based nano‐photocatalysts with high photocatalytic activities for efficient fuel production and environmental remediation