System design and measurements of flux concentrator and its solid-state modulator for CEPC positron source

Positron sources are one of the most important components of the injector of a circular electron positron collector(CEPC).The CEPC is designed as an e^(+)e^(−)collider for a Higgs factory.Its accelerator system is composed of 100-km-long storage rings and an injector.The design goal of the positron source is to obtain positron beams with a bunch charge of 3 nC.The flux concentrator(FC)is one of the cores of the positron source.This paper reports the design,development,and measurements of an FC prototype system.The prototype includes an FC and an all-solid-state high-current pulse modulator.Preliminary tests show that the peak current on the FC can reach 15.5 kA,and the peak magnetic field can reach 6.2 T.The test results are consistent with the theoretical simulation.The FC system fulfills the requirements of the CEPC positron source as well as provides a reference for the development of similar devices both domestically and abroad.

Seasonal and diurnal variations in N2O concentrations and fluxes from three eutrophic rivers in Southeast China

This study was performed at three eutrophic rivers in Southeast China aiming to determine the magnitude and patterns of dissolved N2O concentrations and fluxes over a seasonal （in 2009） and diurnal （24 h） temporal scale.The results showed that N2O concentrations varied from 0.28 to 0.38 （mean 0.32±0.04）,0.29 to 0.46 （mean 0.37±0.07）,and 2.07 to 3.47 （mean 2.84±0.63） μg N-N2O L-1 in the Fengle,Hangbu and Nanfei rivers,respectively,in the diurnal study performed during the summer of 2008.The study found that mean N2O concentration and estimated N2O flux （67.89 ± 6.71 μg N-N2O m-2 h-1） measured from the Nanfei River with serious urban wastewater pollution was significantly higher than those from the Fengle and the Hangbu Rivers with agricultural runoff.In addition,the seasonal study during June and December of 2009 also showed that the mean N2O concentration （10.59±14.67 μg N-N2O L-1） and flux （236.87±449.74 μg N-N2O m-2 h-1） observed from the Nanfei River were significantly higher than those from the other two rivers.Our study demonstrated both N2O concentrations and fluxes exhibited seasonal and diurnal fluctuations.Over three consecutive days during the summer of 2008,N2O accumulation rates varied within the range of 3.91-7.21,2.76-15.71,and 3.23-30.03 μg N-N2O m-2 h-1 for the Fengle,Hangbu and Nanfei Rivers,respectively,and exponentially decreased with time.

Ozone concentrations, flux and potential effect on yield during wheat growth in the NorthwestShandong Plain of China

Ozone（O3） concentration and flux（Fo） were measured using the eddy covariance technique over a wheat field in the Northwest-Shandong Plain of China. The O3-induced wheat yield loss was estimated by utilizing O3exposure-response models. The results showed that：（1） During the growing season（7 March to 7 June, 2012）, the minimum（16.1 ppb V） and maximum（53.3 ppb V）mean O3 concentrations occurred at approximately 6：30 and 16：00, respectively. The mean and maximum of all measured O3 concentrations were 31.3 and 128.4 ppb V, respectively. The variation of O3 concentration was mainly affected by solar radiation and temperature.（2） The mean diurnal variation of deposition velocity（V d） can be divided into four phases, and the maximum occurred at noon（12：00）. Averaged V d during daytime（6：00–18：00） and nighttime（18：00–6：00） were 0.42 and 0.14 cm/sec, respectively. The maximum of measured V d was about1.5 cm/sec. The magnitude of V d was influenced by the wheat growing stage, and its variation was significantly correlated with both global radiation and friction velocity.（3） The maximum mean F o appeared at 14：00, and the maximum measured F o was-33.5 nmol/（m^2·sec）. Averaged F o during daytime and nighttime were-6.9 and-1.5 nmol/（m^2·sec）, respectively.（4） Using O3 exposure-response functions obtained from the USA, Europe, and China, the O3-induced wheat yield reduction in the district was estimated as 12.9% on average（5.5%–23.3%）. Large uncertainties were related to the statistical methods and environmental conditions involved in deriving the exposure-response functions.

CONCENTRATION AND FLUX OF CO_2, TURBULENCE FLUXES AND RADIATION BALANCE IN THE NEAR SURFACE LAYER OVER WHEAT FIELD

The gradient of CO_2 concentration, photosynthetically active radiation (PAR). net radiation. soil heat flux, profiles of wind speed, and air temperature and humidity were measured above a wheat field during May and June 1985 at Beijing Agro-Ecosystems Experimental Station. Beijing, China. Fluxes of carbon dioxide, sensible heat, latent heat and momentum were calculated by using the aerodynamic method. The observation site. equipment, calibration techniques, the errors associated with the measurement, and the computational procedures are described. The results show that the diurnal variations of amplitude of CO_2 concentrations were 103.8 to 27. 0. 86. 3 to 22.8 and 69.8 to 11.6 ppm: the average CO_2 concentrations were 331.5. 339.9 and 364.6 ppm for the photosynthesis type, and 369.6. 364.0 and 375.2 ppm for the respiration type at 1. 2 and 10 m above surface, respectively, from May 14 to June 15. In the daytime, transfer direction of the CO_2 fluxes and gradients is from air to crop canopy, and at noon (1100 to 1300 BT (Beijing Time)) the transfer rate reaches negative maximum value. At night, transfer of CO_2 fluxes and gradients is in the reversed direction and reaches positive maximum in the early morning (0400 to 0600 BT). There are strong negative correlations between CO_2 flux and the net radiation (Rn), available energy (H+LE). photosynthetically active radiation (PAR) and momentum flux (τ).

Boosting the energy harvesting performance of cantilever structured magneto-mechano-electric generator by controlling magnetic flux intensity on magnet proof mass

A cantilever-structured magneto-mechano-electric(MME)generator comprising a magnetoelectric composite with a magnet proof mass is a potential candidate for powering autonomous wireless sensor networks.Recently,the concept of a magnetic flux concentrator(MFC)to enhance the output performance of the MME generator by focusing the ultralow-intensity magnetic field into the MME generator was introduced.However,the MFC-concentrated magnetic flux mostly focused on the end tip of the MME cantilever rather than at the magnet proof mass located on the cantilever beam.Considering that the torque generated by the magnet proof mass contributes more than half of the output power of an MME generator,optimizing the volume and position of the proof-mass with MFC is crucial for better performance.Furthermore,a smaller proof-mass is desirable for the long-term reliability of cantilevertype harvesters.Hence,we investigated the effect of the position and weight(volume)of the magnet proof mass with respect to the MFC on the output performance of the MME generator through finite element analysis and experiments.The MME generator with the lighter magnet proof mass at the optimized position generated a maximum power of 5.35 mW under a 10 Oe magnetic field,which was 210%of that of the MME configuration used in our previous study.Furthermore,the MME generator showed broadband characteristics around the practical frequency of 60 Hz,which could provide more freedom to design the harvester with high performance.

Design of square-shaped heat flux cloaks and concentrators using method of coordinate transformation

A square-shaped heat flux cloak and a square-shaped heat flux concentrator have been designed the- oretically according to the invariance symmetry of steady state thermal conductive equation. The direction of heat flux in these devices can be modulated as desired. Using the method of coordinate transformation, the inhomogeneous and anisotropic thermal conductivity in the transformation region have been acquired. Two-dimensional finite element simulations were performed to confirm the theoretical results.

A passive current sensor employing self-biased magnetoelectric transducer and high-permeability nanocrystalline flux concentrator

A passive current sensor,consisting of SmFe_(2)/PZT/SmFe_(2)self-biased magnetoelectric(ME)composite and Fe_(73.5)Cu_(1)Nb_(3)Si_(13.5)B_(9)nanocrystalline flux concentrator for weak current detection at power-line frequency,was fabricated and characterized.Giant magnetostrictive material of SmFe_(2)plate with large anisotropic constant provides a huge internal anisotropic field to bias the ME transducer in closed magnetic loop.Consequently,the additional magnetomotive force induced by the internal field and the corresponding increased effective permeabil-ity contribute to the improvement of the sensitivity.Experimental results demonstrate that the presented sensor has a higher sensitivity of 152 mV·A^(-1)at 50 Hz with a slight nonlinearity of~0.01%full scale(FS)and matches well with the predicted value.This presented current-sensing device exhibits approximately 2.3 times higher sensitivity than that of conventional ME composite with[Pb(Zr_(0.48),Ti_(0.52)O_(3)](PZT)and Terfenol-D plates serving as a key sensitive component.In addition,time stabilities of the presented sensor were evaluated for a long period of 72 h and analyzed through mathematical statistics method,and favorable stabilities with an uncertainty of 0.5μV are obtained in continuous 1 h testing.These results provide a significant advancement toward promising application of the tri-layer self-biased ME laminate for power-line elec-tric cords monitoring.

COATS:Comprehensive observation on the atmospheric boundary layer three-dimensional structure during haze pollution in the North China Plain

The North China Plain(NCP)is troubled by severe haze pollution and the evolution of haze pollution is closely related to the atmospheric boundary layer(ABL).However,experimental and theoretical studies on the physical-chemical processes of the ABL in the NCP are lacking,with many scientific problems to be addressed.To solve these problems,the Comprehensive Observation on the Atmospheric boundary layer Three-dimensional Structure(COATS)during haze pollution was carried out in the NCP from 2016 to 2020.The COATS experiment adopted a"point-line-surface"spatial layout,obtaining both spatial-temporal profiles of the meteorological and environmental elements in the ABL and the turbulent transport data of fine particulate matter(PM_(2.5))in winter and summer.The research achievements are as follows.The spatial-temporal distribution characteristics of the ABL structure and PM_(2.5)concentrations in NCP were determined.The typical thermal structure of persistent heavy haze events and the pollutant removal mechanism by low-level jets were revealed.It was determined that the spatial structure of the ABL adjusted by the Taihang Mountains is responsible for the heterogeneous distribution of haze pollution in the NCP,and that mountain-induced vertical circulations can promote the formation of elevated pollution layers.The restraints of the atmospheric internal boundaries on horizontal diffusion of pollutants were emphasized.The contribution of the ABL to haze pollution in winter and summer was qualitatively compared and quantitatively estimated.The turbulent transport nature behind the relationship between the atmospheric boundary layer height(ABLH)and surface PM_(2.5)concentrations was analyzed.The concept of"aerosol accumulation layer"was defined,and the applicability of the material method in determining ABLH was clarified.A measurement system for obtaining the turbulent flux of PM_(2.5)concentrations was developed,and the turbulence characteristics of PM_(2.5)concentrations were demonstrated.The COATS experiment is of great theoretical significance for thoroughly understanding the physical mechanisms of the ABL during haze pollution and filling the knowledge gap on the impacts of the ABL three-dimensional structure on haze pollution.The results of this study are conducive to the improvement and development of ABL parameterization schemes and serve as a scientific basis for formulating regional pollution prevention and control measures.

A hybrid magnetometer towards femtotesla sensitivity under ambient conditions

Detecting magnetic field is of great importance for many applications,such as magnetoencephalography and underground prospecting.There have been many magnetometers being widely used since the age of Hall magnetometer.One of the magnetometers,the superconducting quantum interference device,is capable of measuring femtotesla magnetic fields at cryogenic temperature.However,a solid-state magnetometer with femtotesla sensitivity under ambient conditions remains elusive.Here we present a hybrid magnetometer based on the ensemble nitrogen-vacancy centers in diamond with the sensitivity of(195±60)fT/Hz^(1/2)under ambient conditions,which can be further advanced to 11 fT/Hz^(1/2)at 100 Hz with cutting-edge fabrication technologies.Our method will find potential applications in biomagnetism and geomagnetism.

Fabrication and performance of PET mesh enhanced cellulose acetate membranes for forward osmosis

Polyethylene terephthalate mesh（PET） enhanced cellulose acetate membranes were fabricated via a phase inversion process. The membrane fabrication parameters that may affect the membrane performance were systematically evaluated including the concentration and temperature of the casting polymer solution and the temperature and time of the evaporation, coagulation and annealing processes. The water permeability and reverse salt flux were measured in forward osmosis（FO） mode for determination of the optimal membrane fabrication conditions. The optimal FO membrane shows a typical asymmetric sandwich structure with a mean thickness of about 148.2 μm. The performance of the optimal FO membrane was tested using 0.2 mol/L Na Cl as the feed solution and 1.5 mol/L glucose as the draw solution. The membrane displayed a water flux of 3.47 L/（m2·hr） and salt rejection of95.48% in FO mode. While in pressure retarded osmosis（PRO） mode, the water flux was4.74 L/（m2·hr） and salt rejection 96.03%. The high ratio of water flux in FO mode to that in PRO mode indicates that the fabricated membrane has a lower degree of internal concentration polarization than comparable membranes.