The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin fi...The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies(0.5–30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.展开更多
Paul Scherrer Institut hosts the Proton Irradiation Facility used for radiation effects studies and exposure tests in preparation of satellite missions for the European Space Agency. The facility allows for realistic ...Paul Scherrer Institut hosts the Proton Irradiation Facility used for radiation effects studies and exposure tests in preparation of satellite missions for the European Space Agency. The facility allows for realistic simulation of the space proton spectra in the energy range from 6 MeV up to 230 MeV with exposure fluxes ranging from very low up to as high as 109 p/cm2/sec. Recently, approved ESA mission to Jupiter—JUICE—also brought a need for tests with high energy electron beams. For this purpose, another facility was established in the PSI secondary beam area piM1. Secondary particles are produced on the thick carbon target hit by energetic proton beam. Dedicated beam optics enables selection of the particle charge and momentum and guides them to the tests area. Characterization of electron beams at various momenta was performed with respect to their intensity, profiles and contamination by pions and muons. Electron fluxes ranging from 1.5 × 103/cm2/s at 20 MeV/c to 2.3 × 106/cm2/s at 345 MeV/c with gaussian beam profiles with FWHM of about 4 cm were measured. Beam contamination with heavier particles becomes negligible for all momenta lower than 115 MeV/c. This allows for using them for components and shielding characterization and detector calibration experiments. Several such experiments have been already performed utilizing available beam time of few weeks per year.展开更多
Batteries,fuel cells,and supercapacitors are electrochemical devices already on the market and still need a boost in kinetics to match the high energy density demand of applications.Perovskites have attracted the scie...Batteries,fuel cells,and supercapacitors are electrochemical devices already on the market and still need a boost in kinetics to match the high energy density demand of applications.Perovskites have attracted the scientific community's attention in the last decade due to their electrocatalytic activity,chemical and structural properties,tunability,low cost,and scalability.Efforts have been made to understand the active sites and the operational mechanisms in perovskite oxides to shape them as an electrocatalyst in advanced energy devices.Understanding the role of perovskites is the key to engineering more controlled and efficient electrocatalysts via chemical synthesis,and there is still much to do.This review highlights the use of perovskites in different energy storage and conversion systems.The A,B,and A&B doping-site effects are analyzed to understand the opportunities and challenges related to this class of materials.In addition,the synthesis methods and the properties related to the doping site are described and summarized.展开更多
Low-level radio frequency(LLRF)systems stabilize the electromagnetic field in the RF cavities used for beam acceleration in particle accelerators.Reliable,accurate,and precise detection of RF amplitude and phase is pa...Low-level radio frequency(LLRF)systems stabilize the electromagnetic field in the RF cavities used for beam acceleration in particle accelerators.Reliable,accurate,and precise detection of RF amplitude and phase is particularly important to achieve high field stability for pulsed accelerators of free-electron lasers(FEL).The digital LLRF systems employ analog-to-digital converters to sample the frequency down-converted RF signal and use digital demodulation algorithms to calculate the RF amplitude and phase.Different sampling strategies and demodulation algorithms have been developed for these purposes and are introduced in this paper.This article focuses on advanced topics concerning RF detection,including accurate RF transient measurement,wideband RF detection,and RF detection with an asynchronous trigger,local oscillator,or clock.The analysis is based on the SwissFEL measurements,but the algorithms introduced are general for RF signal detection in particle accelerators.展开更多
Swiss FEL is a free electron laser(FEL) under commissioning at the Paul Scherrer Institut(PSI) in Switzerland. Digital low-level RF(LLRF) systems are used in Swiss FEL to control more than 30 RF stations with either s...Swiss FEL is a free electron laser(FEL) under commissioning at the Paul Scherrer Institut(PSI) in Switzerland. Digital low-level RF(LLRF) systems are used in Swiss FEL to control more than 30 RF stations with either standing wave cavities(e.g. RF gun) or travelling wave structures working at different frequencies. After conditioned to desired power levels, the RF stations need to be setup for beam operation and the LLRF parameters need to be optimized for maximizing the beam stability. Several beam-based algorithms were developed to facilitate the setup, calibration and optimization of the Swiss FEL RF stations for beam operation. The algorithms were implemented as automation procedures in the framework of Experimental Physics and Industrial Control System(EPICS) and were used in commissioning and daily operation of Swiss FEL. In this paper, the algorithms and the implementation will be introduced together with the test results during the commissioning of SwissFEL.展开更多
Intensive measurements were conducted in Xi’an,China before and during a COVID-19 lockdown period to investigate how changes in anthropogenic emissions affected the optical properties and radiative effects of brown c...Intensive measurements were conducted in Xi’an,China before and during a COVID-19 lockdown period to investigate how changes in anthropogenic emissions affected the optical properties and radiative effects of brown carbon(BrC)aerosol.The contribution of BrC to total aerosol light absorption during the lockdown(13%-49%)was higher compared with the normal period(4%-29%).Mass absorption cross-sections(MACs)of specific organic aerosol(OA)factors were calculated from a ridge regression model.Of the primary OA(POA),coal combustion OA(CCOA)had the largest MACs at all tested wave-lengths during both periods due to high molecular-weight BrC chromophores;that was followed by biomass burning OA(BBOA)and hydrocarbon-like OA(HOA).For secondary OA(SOA),the MACs of the lessoxidized oxygenated OA(OOA)species(LO-OOA)atλ=370-590 nm were higher than those of more-oxidized OOA(MO-OOA)during both periods,presumably due to chromophore bleaching.The largest contributor to BrC absorption at the short wavelengths was CCOA during both periods,but BrC absorption by LO-OOA and MO-OOA became dominant at longer wavelengths during the lockdown.The estimated radiation forcing efficiency of BrC over 370-600 nm increased from 37.5 W·gduring the normal period to 50.2 W·gduring the lockdown,and that enhancement was mainly caused by higher MACs for both LO-OOA and MO-OOA.This study provides insights into the optical properties and radiative effects of source-specific BrC aerosol when pollution emissions are reduced.展开更多
Maximally-localized Wannier functions(MLWFs)are broadly used to characterize the electronic structure of materials.Generally,one can construct MLWFs describing isolated bands(e.g.valence bands of insulators)or entangl...Maximally-localized Wannier functions(MLWFs)are broadly used to characterize the electronic structure of materials.Generally,one can construct MLWFs describing isolated bands(e.g.valence bands of insulators)or entangled bands(e.g.valence and conduction bands of insulators,or metals).Obtaining accurate and compact MLWFs often requires chemical intuition and trial and error,a challenging step even for experienced researchers and a roadblock for high-throughput calculations.Here,we present an automated approach,projectability-disentangled Wannier functions(PDWFs),that constructs MLWFs spanning the occupied bands and their complement for the empty states,providing a tight-binding picture of optimized atomic orbitals in crystals.Key to the algorithm is a projectability measure for each Bloch state onto atomic orbitals,determining if that state should be kept identically,discarded,or mixed into the disentanglement.We showcase the accuracy on a test set of 200 materials,and the reliability by constructing 21,737 Wannier Hamiltonians.展开更多
The transport of colloids and radionuclides is sophisticated because of the variety of charge properties between colloidal particles and host subsurface media, which causes great difficulty in establishing a reliable ...The transport of colloids and radionuclides is sophisticated because of the variety of charge properties between colloidal particles and host subsurface media, which causes great difficulty in establishing a reliable model of radionuclides migration by taking the colloid phase into consideration. In this work,the co-transport of illite colloids(IC) and Eu(Ⅲ) in the quartz sand and iron-coated sand porous media was investigated by column experiments to address the predominant mechanism of charge properties on co-transport. Results showed that Eu(Ⅲ) transport was driven by the illite colloids and electrostatic interaction was critical in governing the co-transport patterns. The promotion of Eu(Ⅲ) transport by IC was attenuated in the iron-coated sand systems;more IC-Eu(Ⅲ) complexes were retained uniformly in the column. The pore throat shrinkage caused by electrostatic attachment between aggregated IC and iron oxides exacerbated the physical straining and size exclusion effect of IC-Eu(Ⅲ) complexes. An aggravated irreversible retention of IC-Eu(Ⅲ) was detected in iron-coated sand column due to the electrostatic attraction of IC-Eu(Ⅲ) to host media. The findings are essential for improving the understanding on the potential transport, retention and release risk of colloids associated radionuclides, and imply that the positively charged permeable reactive barrier is an effective strategy to reduce the transport risk of colloid associated radionuclides.展开更多
Maximally localized Wannier functions(MLWFs)are widely used in electronic-structure calculations.We have recently developed automated approaches to generate MLWFs that represent natural tight-binding sets of atomic-li...Maximally localized Wannier functions(MLWFs)are widely used in electronic-structure calculations.We have recently developed automated approaches to generate MLWFs that represent natural tight-binding sets of atomic-like orbitals;these describe accurately both the occupied states and the complementary unoccupied ones.For many applications,it is required to use MLWFs that describe instead certain target groups of bands:the valence or the conduction bands,or correlated manifolds.Here,we start from these tight-binding sets of MLWFs,and mix them using a combination of parallel transport and maximal localization to construct manifold-remixed Wannier functions(MRWFs):these are orthogonal sets of MLWFs that fully and only span desired target submanifolds.The algorithm is simple and robust,and is showcased here in reference applications(silicon,MoS_(2),and SrVO_(3))and in a mid-throughput study of 77 insulators.展开更多
The automation of ab initio simulations is essential in view of performing high-throughput(HT)computational screenings oriented to the discovery of novel materials with desired physical properties.In this work,we prop...The automation of ab initio simulations is essential in view of performing high-throughput(HT)computational screenings oriented to the discovery of novel materials with desired physical properties.In this work,we propose algorithms and implementations that are relevant to extend this approach beyond density functional theory(DFT),in order to automate many-body perturbation theory(MBPT)calculations.Notably,an algorithm pursuing the goal of an efficient and robust convergence procedure for GW and BSE simulations is provided,together with its implementation in a fully automated framework.This is accompanied by an automatic GW band interpolation scheme based on maximally localized Wannier functions,aiming at a reduction of the computational burden of quasiparticle band structures while preserving high accuracy.The proposed developments are validated on a set of representative semiconductor and metallic systems.展开更多
Ambient PM2.5 samples were collected at four sites in Xiamen, including Gulangyu （GLY）. Hongwen （HW）, Huli （HL） and Jimei （JM） during January, April, July and October 2013. Local source samples were obtained f...Ambient PM2.5 samples were collected at four sites in Xiamen, including Gulangyu （GLY）. Hongwen （HW）, Huli （HL） and Jimei （JM） during January, April, July and October 2013. Local source samples were obtained from coal burning power plants, industries, motor vehicles, biomass burning, fugitive dust, and sea salt for the source apportionment studies. The highest value of PM2.5 mass concentration and species related to human activities （SO42- , NO3 , Pb, Ni, V, Cu, Cd, organic carbon （OC） andelemental carbon （EC）） were found in the ambient-samples from HL, and t-he highest and lowest loadings of PM2.5 and its components occurred in winter and summer, respectively. The reconstructed mass balance indicated that ambient PM2.5 consisted of 24% OM （organic matter）, 23% sulfate, 14% nitrate, 9% ammonium, 9% geological material, 6% sea salt, 5% EC and 10% others. For the source profiles, the dominant components were OC for coal burning, motor vehicle, biomass burning and sea salt; SO42 for industry; and crustal elements for fugitive dust. Source contributions were calculatedusing a chemical mass＇balance （CMB） model basedon ambient PM2.5 concentrations and the source profiles. GLY was characterized by high contributions from secondary sulfate and cooking, while HL and JM were most strongly affected by motor vehicle emissions, and biomass burning and fugitivedust, respectively. The CMB results-indicated that PM2.5 from Xiamen is composed of 27.4% secondary inorganic components, 20.8% motor vehicle emissions, 11.7% fugitive dust, 9.9% sea salt, 9.3% coal burning, 5.0% biomass burning, 3.1% industry and 6.8% others.展开更多
A distinctive kind of organic carbon aerosol that could absorb ultraviolet-visible radiation is called brown carbon(Br C),which has an important positive influence on radiative budget and climate change.In this work,w...A distinctive kind of organic carbon aerosol that could absorb ultraviolet-visible radiation is called brown carbon(Br C),which has an important positive influence on radiative budget and climate change.In this work,we reported the absorption properties and potential source of Br C based on a seven-wavelength aethalometer in the winter of 2018–2019 at an urban site of Sanmenxia in Fenwei Plain in central China.Specifically,the mean value of Br C absorption coefficient was 59.6±36.0 Mm^(-1) at 370 nm and contributed 37.7%to total absorption,which made a significant impact on visibility and regional environment.Absorption coefficients of Br C showed double-peak pattern,and Br C had shown small fluctuations under haze days compared with clean days.As for the sources of Br C,Br C absorption coefficients expressed strong correlations with element carbon aerosols and primary organic carbon aerosols,indicating that most of Br C originated from primary emissions.The linear correlations between trace metal elements(K,As,Fe,Mn,Zn,and Pb)and Br C absorption coefficients further referred that the major sources of Br C were primary emissions,like coal burning,biomass burning,and vehicle emissions.The moderate relationship between Br C absorption coefficients and secondary organic aerosols suggested that secondary production of Br C also played an important role.The 120 hr backward air mass trajectories analysis and concentration-weighted trajectories analysis were also used to investigate potential sources of Br C in and around this area,which inferred most parts of Br C were derived from local emissions.展开更多
Understanding the formation mechanisms of secondary air pollution is very important for the formulation of air pollution control countermeasures in China.Thus,a large-scale outdoor atmospheric simulation smog chamber ...Understanding the formation mechanisms of secondary air pollution is very important for the formulation of air pollution control countermeasures in China.Thus,a large-scale outdoor atmospheric simulation smog chamber was constructed at Chinese Research Academy of Environmental Sciences(the CRAES Chamber),which was designed for simulating the atmospheric photochemical processes under the conditions close to the real atmospheric environment.The chamber consisted of a 56-m^(3) fluorinated ethylene propylene(FEP) Teflon film reactor,an electrically-driven stainless steel alloy shield,an auxiliary system,and multiple detection instrumentations.By performing a series of characterization experiments,we obtained basic parameters of the CRAES chamber,such as the mixing ability,the background reactivity,and the wall loss rates of gaseous compounds(propene,NO,NO_(2),ozone) and aerosols(ammonium sulfate).Oxidation experiments were also performed to study the formation of ozone and secondary organic aerosol(SOA),including α-pinene ozonolysis,propene and 1,3,5-trimethylbenzene photooxidation.Temperature and seed effects on the vapor wall loss and SOA yields were obtained in this work:higher temperature and the presence of seed could reduce the vapor wall loss;SOA yield was found to depend inversely on temperature,and the presence of seed could increase SOA yield.The seed was suggested to be used in the chamber to reduce the interaction between the gas phase and chamber walls.The results above showed that the CRAES chamber was reliable and could meet the demands for investigating tropospheric chemistry.展开更多
Layered alkali-containing 3d transition-metal oxides are of the utmost importance in the use of electrode materials for advanced energy storage applications such as Li-,Na-,or K-ion batteries.A significant challenge i...Layered alkali-containing 3d transition-metal oxides are of the utmost importance in the use of electrode materials for advanced energy storage applications such as Li-,Na-,or K-ion batteries.A significant challenge in the field of materials chemistry is understanding the dynamics of the chemical reactions between alkali-free precursors and alkali species during the synthesis of these compounds.In this study,in situ high-resolution synchrotron-based X-ray diffraction was applied to reveal the Li/Na/K-ion insertion-induced structural transformation mechanism during high-temperature solid-state reaction.The in situ diffraction results demonstrate that the chemical reaction pathway strongly depends on the alkali-free precursor type,which is a structural matrix enabling phase transi-tions.Quantitative phase analysis identifies for the first time the decomposition of lithium sources as the most critical factor for the formation of metastable intermediates or impurities during the entire process of Li-rich layered Li[Li_(0.2)Ni_(0.2)Mn_(0.6)]O_(2) formation.Since the alkali ions have different ionic radii,Na/K ions tend to be located on prismatic sites in the defective layered structure(Na_(2/3-x)[Ni_(0.25)Mn_(0.75)]O_(2) or K_(2/3-x)[Ni_(0.25)Mn_(0.75)]O_(2))during calcination,whereas the Li ions prefer to be localized on the tetrahedral and/or octahedral sites,forming O-type structures.展开更多
A new simple digital positron lifetime spectrometer has been developed. It includes a DRS4 waveform digitizing board and two scintillation detectors based on the XP2020Q photomultiplier tubes and LaBr3 scintillators. ...A new simple digital positron lifetime spectrometer has been developed. It includes a DRS4 waveform digitizing board and two scintillation detectors based on the XP2020Q photomultiplier tubes and LaBr3 scintillators. The DRS4 waveform digitizing can handle small pulses, down to few tens of millivolts, and its time scale linearity and stability are very good. The new system has reached a 206 ps time resolution, which is better than the conventional analog apparatus using the same detectors. These improvements make this spectrometer more simple and convenient in comparison with other spectrometers, and it can be applied to the other scintillation timing measurements with picosecond accuracy.展开更多
The Energy-related Severe Accident Database(ENSAD)is the most authoritative resource for comparative risk analysis of accidents in the energy sector.Although ENSAD contains comprehensive,worldwide data,it is a non-spa...The Energy-related Severe Accident Database(ENSAD)is the most authoritative resource for comparative risk analysis of accidents in the energy sector.Although ENSAD contains comprehensive,worldwide data,it is a non-spatial database in Microsoft Access format.Therefore,spatial characteristics of the data cannot be fully utilised as well as analysed directly.Based on these premises,a new web-based version of ENSAD with GIS-capabilities–named ENSAD v2.0–is designed and developed using state-of-the-art,open source technologies.The ENSAD v2.0 consists of two main components,i.e.a spatial database and a responsive web application.For the spatial database,the current accident data are georeferenced and migrated from Microsoft Access,using a tiered approach.The responsive web application can be accessed from desktops as well as mobile devices,and provides both a 2D and 3D mapping platform that is developed on cloud-based,serverless architecture.ENSAD v2.0 also allows assigning different user roles with specific access rights,and a public version with advanced visualisation capabilities has also been developed.Lastly,a case study was carried out using a spatial analysis to visualise the potential impact radius of a natural gas pipeline explosion and to assess its consequences in terms of economic damage and casualties.展开更多
Geomagnetic disturbances(GMDs)are known to disturb power system equipment performance.The danger is associated with geomagnetically induced currents(GICs)occurring at the Earth's surface during GMD.GICs do not end...Geomagnetic disturbances(GMDs)are known to disturb power system equipment performance.The danger is associated with geomagnetically induced currents(GICs)occurring at the Earth's surface during GMD.GICs do not endanger power system operation conditions by themselves.The main challenge posed by GICs to power system states is the change in power system equipment operation conditions provoked by GIC flow.The primary avenue of blackout caused by GMDs is through power transformers.This,in turn,can impair the operation of other power system equipment such as syn-chronous machines.Modern powerful synchronous machines are not designed and engineered to cope with the negative impacts of GMDs.Moreover,the actual legal norms are inadequate in this case.Enhancing the grid's resiliency to such an event is highly interesting to the industry.The physical processes in synchronous machine windings triggered by GICs and limitations brought to power grid operations are described.First,the idea of the impact of GMDs on the power grid operation is described.The analysis of the impact of GMDs on synchronous machines is performed in the second section.In the end,the power system response under GMDs is studied.展开更多
基金a scholarship from the China Scholarship Council (CSC)financial support from PSI for her stay at PSI
文摘The low-energy muon facility at PSI provides nearly fully polarized positive muons with tunable energies in the ke V range to carry out muon spin rotation(LE-μSR)experiments with nanometer depth resolution on thin films,heterostructures, and near-surface regions. The low-energy muon beam is focused and transported to the sample by electrostatic lenses. In order to achieve a minimum beam spot size at the sample position and to enable the steering of the beam in the horizontal and vertical direction, a special electrostatic device has been implemented close to the sample position. It consists of a cylinder at ground potential followed by four conically shaped electrodes,which can be operated at different electric potential. In LE-μSR experiments, an electric field at the sample along the beam direction can be applied to accelerate/decelerate muons to different energies(0.5–30 keV). Additionally, a horizontal or vertical magnetic field can be superimposed for transverse or longitudinal field μSR experiments. The focusing properties of the conical lens in the presence of these additional electric and magnetic fields have been investigated and optimized by Geant4 simulations. Some experimental tests were also performed and show that the simulation well describes the experimental setup.
文摘Paul Scherrer Institut hosts the Proton Irradiation Facility used for radiation effects studies and exposure tests in preparation of satellite missions for the European Space Agency. The facility allows for realistic simulation of the space proton spectra in the energy range from 6 MeV up to 230 MeV with exposure fluxes ranging from very low up to as high as 109 p/cm2/sec. Recently, approved ESA mission to Jupiter—JUICE—also brought a need for tests with high energy electron beams. For this purpose, another facility was established in the PSI secondary beam area piM1. Secondary particles are produced on the thick carbon target hit by energetic proton beam. Dedicated beam optics enables selection of the particle charge and momentum and guides them to the tests area. Characterization of electron beams at various momenta was performed with respect to their intensity, profiles and contamination by pions and muons. Electron fluxes ranging from 1.5 × 103/cm2/s at 20 MeV/c to 2.3 × 106/cm2/s at 345 MeV/c with gaussian beam profiles with FWHM of about 4 cm were measured. Beam contamination with heavier particles becomes negligible for all momenta lower than 115 MeV/c. This allows for using them for components and shielding characterization and detector calibration experiments. Several such experiments have been already performed utilizing available beam time of few weeks per year.
基金support from FAPESP (Sao Paulo Research Foundation,Grant Numbers 2014/02163-7,2017/11958-1,2020/14968-0)CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico,301486/2016-6)the support given by ANP (Brazil’s National Oil,Natural Gas and Biofuels Agency)through the R&D levy regulation。
文摘Batteries,fuel cells,and supercapacitors are electrochemical devices already on the market and still need a boost in kinetics to match the high energy density demand of applications.Perovskites have attracted the scientific community's attention in the last decade due to their electrocatalytic activity,chemical and structural properties,tunability,low cost,and scalability.Efforts have been made to understand the active sites and the operational mechanisms in perovskite oxides to shape them as an electrocatalyst in advanced energy devices.Understanding the role of perovskites is the key to engineering more controlled and efficient electrocatalysts via chemical synthesis,and there is still much to do.This review highlights the use of perovskites in different energy storage and conversion systems.The A,B,and A&B doping-site effects are analyzed to understand the opportunities and challenges related to this class of materials.In addition,the synthesis methods and the properties related to the doping site are described and summarized.
文摘Low-level radio frequency(LLRF)systems stabilize the electromagnetic field in the RF cavities used for beam acceleration in particle accelerators.Reliable,accurate,and precise detection of RF amplitude and phase is particularly important to achieve high field stability for pulsed accelerators of free-electron lasers(FEL).The digital LLRF systems employ analog-to-digital converters to sample the frequency down-converted RF signal and use digital demodulation algorithms to calculate the RF amplitude and phase.Different sampling strategies and demodulation algorithms have been developed for these purposes and are introduced in this paper.This article focuses on advanced topics concerning RF detection,including accurate RF transient measurement,wideband RF detection,and RF detection with an asynchronous trigger,local oscillator,or clock.The analysis is based on the SwissFEL measurements,but the algorithms introduced are general for RF signal detection in particle accelerators.
文摘Swiss FEL is a free electron laser(FEL) under commissioning at the Paul Scherrer Institut(PSI) in Switzerland. Digital low-level RF(LLRF) systems are used in Swiss FEL to control more than 30 RF stations with either standing wave cavities(e.g. RF gun) or travelling wave structures working at different frequencies. After conditioned to desired power levels, the RF stations need to be setup for beam operation and the LLRF parameters need to be optimized for maximizing the beam stability. Several beam-based algorithms were developed to facilitate the setup, calibration and optimization of the Swiss FEL RF stations for beam operation. The algorithms were implemented as automation procedures in the framework of Experimental Physics and Industrial Control System(EPICS) and were used in commissioning and daily operation of Swiss FEL. In this paper, the algorithms and the implementation will be introduced together with the test results during the commissioning of SwissFEL.
基金financially supported by the Key Research and Development Program of Shaanxi Province(2018-ZDXM3-01)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB40000000)+3 种基金the Sino-Swiss Cooperation on Air Pollution for Better Air(7F-09802.01.02)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2019402)the Sino-Swiss Science and Technology Cooperation(SSSTC)project HAZECHINA(IZLCZ2_169986)the SDC Clean-Air-China Program(7F-09802.01.03)。
文摘Intensive measurements were conducted in Xi’an,China before and during a COVID-19 lockdown period to investigate how changes in anthropogenic emissions affected the optical properties and radiative effects of brown carbon(BrC)aerosol.The contribution of BrC to total aerosol light absorption during the lockdown(13%-49%)was higher compared with the normal period(4%-29%).Mass absorption cross-sections(MACs)of specific organic aerosol(OA)factors were calculated from a ridge regression model.Of the primary OA(POA),coal combustion OA(CCOA)had the largest MACs at all tested wave-lengths during both periods due to high molecular-weight BrC chromophores;that was followed by biomass burning OA(BBOA)and hydrocarbon-like OA(HOA).For secondary OA(SOA),the MACs of the lessoxidized oxygenated OA(OOA)species(LO-OOA)atλ=370-590 nm were higher than those of more-oxidized OOA(MO-OOA)during both periods,presumably due to chromophore bleaching.The largest contributor to BrC absorption at the short wavelengths was CCOA during both periods,but BrC absorption by LO-OOA and MO-OOA became dominant at longer wavelengths during the lockdown.The estimated radiation forcing efficiency of BrC over 370-600 nm increased from 37.5 W·gduring the normal period to 50.2 W·gduring the lockdown,and that enhancement was mainly caused by higher MACs for both LO-OOA and MO-OOA.This study provides insights into the optical properties and radiative effects of source-specific BrC aerosol when pollution emissions are reduced.
基金We acknowledge financial support from the NCCR MARVEL(a National Centre of Competence in Research,funded by the Swiss National Science Foundation,grant No.205602)the Swiss National Science Foundation(SNSF)Project Funding(grant 200021E_206190“FISH4DIET”)The work is also supported by a pilot access grant from the Swiss National Supercomputing Centre(CSCS)on the Swiss share of the LUMI system under project ID“PILOT MC EPFL-NM 01”,a CHRONOS grant from the CSCS on the Swiss share of the LUMI system under project ID“REGULAR MC EPFL-NM 02”,and a grant from the CSCS under project ID s0178.
文摘Maximally-localized Wannier functions(MLWFs)are broadly used to characterize the electronic structure of materials.Generally,one can construct MLWFs describing isolated bands(e.g.valence bands of insulators)or entangled bands(e.g.valence and conduction bands of insulators,or metals).Obtaining accurate and compact MLWFs often requires chemical intuition and trial and error,a challenging step even for experienced researchers and a roadblock for high-throughput calculations.Here,we present an automated approach,projectability-disentangled Wannier functions(PDWFs),that constructs MLWFs spanning the occupied bands and their complement for the empty states,providing a tight-binding picture of optimized atomic orbitals in crystals.Key to the algorithm is a projectability measure for each Bloch state onto atomic orbitals,determining if that state should be kept identically,discarded,or mixed into the disentanglement.We showcase the accuracy on a test set of 200 materials,and the reliability by constructing 21,737 Wannier Hamiltonians.
基金supported by the National Natural Science Foundation of China(Nos.22176077,22006060)the Fundamental Research Funds for the Central Universities(No.lzujbky-2022-sp04)Science and Technology Program of Gansu Province,China(No.20JR10RA615).
文摘The transport of colloids and radionuclides is sophisticated because of the variety of charge properties between colloidal particles and host subsurface media, which causes great difficulty in establishing a reliable model of radionuclides migration by taking the colloid phase into consideration. In this work,the co-transport of illite colloids(IC) and Eu(Ⅲ) in the quartz sand and iron-coated sand porous media was investigated by column experiments to address the predominant mechanism of charge properties on co-transport. Results showed that Eu(Ⅲ) transport was driven by the illite colloids and electrostatic interaction was critical in governing the co-transport patterns. The promotion of Eu(Ⅲ) transport by IC was attenuated in the iron-coated sand systems;more IC-Eu(Ⅲ) complexes were retained uniformly in the column. The pore throat shrinkage caused by electrostatic attachment between aggregated IC and iron oxides exacerbated the physical straining and size exclusion effect of IC-Eu(Ⅲ) complexes. An aggravated irreversible retention of IC-Eu(Ⅲ) was detected in iron-coated sand column due to the electrostatic attraction of IC-Eu(Ⅲ) to host media. The findings are essential for improving the understanding on the potential transport, retention and release risk of colloids associated radionuclides, and imply that the positively charged permeable reactive barrier is an effective strategy to reduce the transport risk of colloid associated radionuclides.
基金We acknowledge financial support from the NCCR MARVEL(a National Centre of Competence in Research,funded by the Swiss National Science Foundation,grant No.205602)the Swiss National Science Foundation(SNSF)Project Funding(grant 200021E_206190“FISH4DIET”)The work is also supported by a pilot access grant from the Swiss National Supercomputing Centre(CSCS)on the Swiss share of the LUMI system under project ID“PILOT MC EPFL-NM 01”,a CHRONOS grant from the CSCS on the Swiss share of the LUMI system under project ID“REGULAR MC EPFL-NM 02”,and a grant from the CSCS under project ID s0178.
文摘Maximally localized Wannier functions(MLWFs)are widely used in electronic-structure calculations.We have recently developed automated approaches to generate MLWFs that represent natural tight-binding sets of atomic-like orbitals;these describe accurately both the occupied states and the complementary unoccupied ones.For many applications,it is required to use MLWFs that describe instead certain target groups of bands:the valence or the conduction bands,or correlated manifolds.Here,we start from these tight-binding sets of MLWFs,and mix them using a combination of parallel transport and maximal localization to construct manifold-remixed Wannier functions(MRWFs):these are orthogonal sets of MLWFs that fully and only span desired target submanifolds.The algorithm is simple and robust,and is showcased here in reference applications(silicon,MoS_(2),and SrVO_(3))and in a mid-throughput study of 77 insulators.
基金This work was supported by:the Centre of Excellence“MaX-Materials Design at the Exascale”funded by European Union(H2020-EINFRA-2015-1,Grant No.676598,H2020-INFRAEDI-2018-1,Grant No.824143,HORIZON-EUROHPC-JU-2021-COE-1,Grant No.101093324)the European Union’s Horizon 2020 research and innovation program(BIG-MAP,Grant No.957189,also part of the BATTERY 2030+initiative,Grant No.957213)+4 种基金SUPER(Supercomputing Unified Platform-Emilia-Romagna)from Emilia-Romagna PORFESR 2014-2020 regional fundsthe Italian national program PRIN20172017BZPKSZ“Excitonic insulator in two-dimensional long-range interacting systems”the ICSC-Centro Nazionale di Ricerca in High Performance Computing,Big Data and Quantum Computing,funded by European Union-NextGenerationEU-PNRR,Missione 4 Componente 2 Investimento 1.4the Swiss National Science Foundation(SNSF)Project Funding(Grant No.200021E_206190“FISH4DIET”)NCCR MARVEL,a National Centre of Competence in Research,funded by the Swiss National Science Foundation(Grant No.205602).Computational time on the Marconi100 and Galileo100 machines at CINECA was provided by the Italian ISCRA program.
文摘The automation of ab initio simulations is essential in view of performing high-throughput(HT)computational screenings oriented to the discovery of novel materials with desired physical properties.In this work,we propose algorithms and implementations that are relevant to extend this approach beyond density functional theory(DFT),in order to automate many-body perturbation theory(MBPT)calculations.Notably,an algorithm pursuing the goal of an efficient and robust convergence procedure for GW and BSE simulations is provided,together with its implementation in a fully automated framework.This is accompanied by an automatic GW band interpolation scheme based on maximally localized Wannier functions,aiming at a reduction of the computational burden of quasiparticle band structures while preserving high accuracy.The proposed developments are validated on a set of representative semiconductor and metallic systems.
基金This work was supported by the Xiamen Environ- mental Protection Special Project （No. 19 （10）, 2013）, Science and Technology Project of Fujian Provincial Environmental Protection Depart- ment （2014）, and also supported by a project from Ministry of Science and Technology （2013FY 112700） and the Natural Science Foundation of China （Grant No. 41673125）.
文摘Ambient PM2.5 samples were collected at four sites in Xiamen, including Gulangyu （GLY）. Hongwen （HW）, Huli （HL） and Jimei （JM） during January, April, July and October 2013. Local source samples were obtained from coal burning power plants, industries, motor vehicles, biomass burning, fugitive dust, and sea salt for the source apportionment studies. The highest value of PM2.5 mass concentration and species related to human activities （SO42- , NO3 , Pb, Ni, V, Cu, Cd, organic carbon （OC） andelemental carbon （EC）） were found in the ambient-samples from HL, and t-he highest and lowest loadings of PM2.5 and its components occurred in winter and summer, respectively. The reconstructed mass balance indicated that ambient PM2.5 consisted of 24% OM （organic matter）, 23% sulfate, 14% nitrate, 9% ammonium, 9% geological material, 6% sea salt, 5% EC and 10% others. For the source profiles, the dominant components were OC for coal burning, motor vehicle, biomass burning and sea salt; SO42 for industry; and crustal elements for fugitive dust. Source contributions were calculatedusing a chemical mass＇balance （CMB） model basedon ambient PM2.5 concentrations and the source profiles. GLY was characterized by high contributions from secondary sulfate and cooking, while HL and JM were most strongly affected by motor vehicle emissions, and biomass burning and fugitivedust, respectively. The CMB results-indicated that PM2.5 from Xiamen is composed of 27.4% secondary inorganic components, 20.8% motor vehicle emissions, 11.7% fugitive dust, 9.9% sea salt, 9.3% coal burning, 5.0% biomass burning, 3.1% industry and 6.8% others.
基金supported by The National Key Research and Development Program of China(No.2017YFC0209500)the National Natural Science Foundation of China(Nos.91744204,41822703,and 91844301)National research program for key issues in air pollution control(No.DQGG-0103)。
文摘A distinctive kind of organic carbon aerosol that could absorb ultraviolet-visible radiation is called brown carbon(Br C),which has an important positive influence on radiative budget and climate change.In this work,we reported the absorption properties and potential source of Br C based on a seven-wavelength aethalometer in the winter of 2018–2019 at an urban site of Sanmenxia in Fenwei Plain in central China.Specifically,the mean value of Br C absorption coefficient was 59.6±36.0 Mm^(-1) at 370 nm and contributed 37.7%to total absorption,which made a significant impact on visibility and regional environment.Absorption coefficients of Br C showed double-peak pattern,and Br C had shown small fluctuations under haze days compared with clean days.As for the sources of Br C,Br C absorption coefficients expressed strong correlations with element carbon aerosols and primary organic carbon aerosols,indicating that most of Br C originated from primary emissions.The linear correlations between trace metal elements(K,As,Fe,Mn,Zn,and Pb)and Br C absorption coefficients further referred that the major sources of Br C were primary emissions,like coal burning,biomass burning,and vehicle emissions.The moderate relationship between Br C absorption coefficients and secondary organic aerosols suggested that secondary production of Br C also played an important role.The 120 hr backward air mass trajectories analysis and concentration-weighted trajectories analysis were also used to investigate potential sources of Br C in and around this area,which inferred most parts of Br C were derived from local emissions.
基金supported by the China Postdoctoral Science Foundation (No.2019M660752)the Beijing Municipal Science&Technology Commission (No.Z181100005418015),LAC/CMA (No.2019B08)+2 种基金the Fundamental Research Funds for Central Public Welfare Scientific Research Institutes of ChinaChinese Research Academy of Environmental Sciences (Nos.GYG5051201,2009GGQD18,2019YSKY-018,2019YSKY-012)the Chinese Academy of Sciences Strategic Leading Science and Technology Project (Class B)(No.XDB05010200)。
文摘Understanding the formation mechanisms of secondary air pollution is very important for the formulation of air pollution control countermeasures in China.Thus,a large-scale outdoor atmospheric simulation smog chamber was constructed at Chinese Research Academy of Environmental Sciences(the CRAES Chamber),which was designed for simulating the atmospheric photochemical processes under the conditions close to the real atmospheric environment.The chamber consisted of a 56-m^(3) fluorinated ethylene propylene(FEP) Teflon film reactor,an electrically-driven stainless steel alloy shield,an auxiliary system,and multiple detection instrumentations.By performing a series of characterization experiments,we obtained basic parameters of the CRAES chamber,such as the mixing ability,the background reactivity,and the wall loss rates of gaseous compounds(propene,NO,NO_(2),ozone) and aerosols(ammonium sulfate).Oxidation experiments were also performed to study the formation of ozone and secondary organic aerosol(SOA),including α-pinene ozonolysis,propene and 1,3,5-trimethylbenzene photooxidation.Temperature and seed effects on the vapor wall loss and SOA yields were obtained in this work:higher temperature and the presence of seed could reduce the vapor wall loss;SOA yield was found to depend inversely on temperature,and the presence of seed could increase SOA yield.The seed was suggested to be used in the chamber to reduce the interaction between the gas phase and chamber walls.The results above showed that the CRAES chamber was reliable and could meet the demands for investigating tropospheric chemistry.
基金the National Natural Science Foundation of China(grant no.22108218)“Young Talent Support Plan”of Xi'an Jiaotong University(71211201010723)+6 种基金This work was financially supported by the China Postdoctoral Science Foundation(Grant No.2021M693813)Guangxi Science and Technology Base and Talents Special Project(Grant No.AD21159007)the Natural Science Foundation of Guangxi(Grant No.2020GXNSFBA297029)the Foundation of Key Laboratory of New Processing Technology for Nonferrous Metal&Materials,Ministry of Education/Guangxi Key Laboratory of Optical and Electronic Materials and Devices,Guilin University of Technology(Contract No.20AA-13)the Foundation of Guilin University of Tech-nology(GLUTQDJJ2020003)High Level Innovation Team and Outstanding Scholar Program of Guangxi Institutes.We acknowledge DESY(Hamburg,Germany),a member of the Helmholtz Association HGF,and Paul Scherrer Institut(Villigen PSI,Switzerland)for the provision of experimental facilitiescontributes to the research performed at CELEST(Center for Electro-chemical Energy Storage Ulm-Karlsruhe)and was supported by the German Research Foundation(DFG)under Project ID 390874152(POLiS Cluster of Excellence).
文摘Layered alkali-containing 3d transition-metal oxides are of the utmost importance in the use of electrode materials for advanced energy storage applications such as Li-,Na-,or K-ion batteries.A significant challenge in the field of materials chemistry is understanding the dynamics of the chemical reactions between alkali-free precursors and alkali species during the synthesis of these compounds.In this study,in situ high-resolution synchrotron-based X-ray diffraction was applied to reveal the Li/Na/K-ion insertion-induced structural transformation mechanism during high-temperature solid-state reaction.The in situ diffraction results demonstrate that the chemical reaction pathway strongly depends on the alkali-free precursor type,which is a structural matrix enabling phase transi-tions.Quantitative phase analysis identifies for the first time the decomposition of lithium sources as the most critical factor for the formation of metastable intermediates or impurities during the entire process of Li-rich layered Li[Li_(0.2)Ni_(0.2)Mn_(0.6)]O_(2) formation.Since the alkali ions have different ionic radii,Na/K ions tend to be located on prismatic sites in the defective layered structure(Na_(2/3-x)[Ni_(0.25)Mn_(0.75)]O_(2) or K_(2/3-x)[Ni_(0.25)Mn_(0.75)]O_(2))during calcination,whereas the Li ions prefer to be localized on the tetrahedral and/or octahedral sites,forming O-type structures.
基金Supported by National Natural Science Foundation of China(11175171,10835006,11105139,10975133)
文摘A new simple digital positron lifetime spectrometer has been developed. It includes a DRS4 waveform digitizing board and two scintillation detectors based on the XP2020Q photomultiplier tubes and LaBr3 scintillators. The DRS4 waveform digitizing can handle small pulses, down to few tens of millivolts, and its time scale linearity and stability are very good. The new system has reached a 206 ps time resolution, which is better than the conventional analog apparatus using the same detectors. These improvements make this spectrometer more simple and convenient in comparison with other spectrometers, and it can be applied to the other scintillation timing measurements with picosecond accuracy.
基金The research was conducted at the Future Resilient Systems(FRS)at the Singapore-ETH Centre(SEC),which was established collaboratively between ETH Zurich and Singapore’s National Research Foundation(FI 370074011)under its Campus for Research Excellence And Technological Enterprise(CREATE)programme.
文摘The Energy-related Severe Accident Database(ENSAD)is the most authoritative resource for comparative risk analysis of accidents in the energy sector.Although ENSAD contains comprehensive,worldwide data,it is a non-spatial database in Microsoft Access format.Therefore,spatial characteristics of the data cannot be fully utilised as well as analysed directly.Based on these premises,a new web-based version of ENSAD with GIS-capabilities–named ENSAD v2.0–is designed and developed using state-of-the-art,open source technologies.The ENSAD v2.0 consists of two main components,i.e.a spatial database and a responsive web application.For the spatial database,the current accident data are georeferenced and migrated from Microsoft Access,using a tiered approach.The responsive web application can be accessed from desktops as well as mobile devices,and provides both a 2D and 3D mapping platform that is developed on cloud-based,serverless architecture.ENSAD v2.0 also allows assigning different user roles with specific access rights,and a public version with advanced visualisation capabilities has also been developed.Lastly,a case study was carried out using a spatial analysis to visualise the potential impact radius of a natural gas pipeline explosion and to assess its consequences in terms of economic damage and casualties.
文摘Geomagnetic disturbances(GMDs)are known to disturb power system equipment performance.The danger is associated with geomagnetically induced currents(GICs)occurring at the Earth's surface during GMD.GICs do not endanger power system operation conditions by themselves.The main challenge posed by GICs to power system states is the change in power system equipment operation conditions provoked by GIC flow.The primary avenue of blackout caused by GMDs is through power transformers.This,in turn,can impair the operation of other power system equipment such as syn-chronous machines.Modern powerful synchronous machines are not designed and engineered to cope with the negative impacts of GMDs.Moreover,the actual legal norms are inadequate in this case.Enhancing the grid's resiliency to such an event is highly interesting to the industry.The physical processes in synchronous machine windings triggered by GICs and limitations brought to power grid operations are described.First,the idea of the impact of GMDs on the power grid operation is described.The analysis of the impact of GMDs on synchronous machines is performed in the second section.In the end,the power system response under GMDs is studied.
